Ultrasonic motor, drive control system, optical apparatus, and vibrator

ABSTRACT

Provided are an ultrasonic motor and a drive control system and the like using the ultrasonic motor. The ultrasonic motor includes an annular vibrator and an annular moving member arranged so as to be brought into pressure-contact with the vibrator. The vibrator includes an annular vibrating plate and an annular piezoelectric element. The piezoelectric element includes an annular piezoelectric ceramic piece, a common electrode arranged on one surface of the piezoelectric ceramic piece, and a plurality of electrodes arranged on the other surface of the piezoelectric ceramic piece. The piezoelectric ceramic piece contains lead in a content of less than 1,000 ppm. The plurality of electrodes include two drive phase electrodes, one or more non-drive phase electrodes, and one or more detection phase electrodes.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an ultrasonic motor, a drive controlsystem and an optical apparatus that use the ultrasonic motor, andfurther, to a vibrator to be used in the ultrasonic motor.

Description of the Related Art

A vibration-type (vibrational wave) actuator includes a vibratorconfigured to excite vibration in an elastic body having an annularshape, an elliptical shape, a bar shape, or the like, which is joined toan electromechanical energy converting element, e.g., a piezoelectricelement, by applying an electric signal, e.g., alternating voltage tothe electromechanical energy converting element. The vibration-typeactuator is used, for example, as an ultrasonic motor configured torelatively move an elastic body (moving member) that is brought intopressure-contact with the vibrator and the vibrator (static member)through use of the drive force of the vibration excited in the vibrator.

Now, an overview of the structure and drive principle of an annularultrasonic motor that is a typical usage form of the vibration-typeactuator is described. In the following description, the term “annular”is intended to mean that an annular article or element can beschematically regarded as a configuration in which a disc having apredetermined thickness includes a circular through hole concentrically.In this case, the dimension of the disc-shaped article or elementcorresponding to the thickness of the disc is referred to as “thickness”of the article or element, and respective surfaces of the annulararticle or element corresponding to both surfaces of the disc that holdthe thickness of the disc are individually or generically referred to as“surfaces” of the article or element.

The annular ultrasonic motor includes an annular vibrator and an annularmoving member that is brought into pressure-contact with the vibrator.The moving member is formed of an elastic body, and a metal is generallyused as a material for the moving member. The vibrator includes anannular vibrating plate and an annular piezoelectric element arranged onone surface of the vibrating plate. The vibrating plate is formed of anelastic body, and a metal is generally used as a material for thevibrating plate. The piezoelectric element includes, on one surface ofan annular piezoelectric ceramics, an electrode divided into a pluralityof regions along the circumferential direction of the annular ring andone common electrode on the other surface thereof. A lead zirconatetitanate-based material is generally used as a material for thepiezoelectric ceramics.

The electrode divided into a plurality of regions includes two regionsforming drive phase electrodes, at least one region forming a detectionphase electrode, and a region forming a non-drive phase electrode, whichis arranged as necessary. Wiring configured to input electric power forapplying an electric field to a corresponding region of the annularpiezoelectric ceramics that is brought into contact with each drivephase electrode is arranged in each drive phase electrode, and thewiring is connected to a power source unit.

A circle that passes through an arbitrary position on the surface of theannular piezoelectric element and shares the center with the annularring is assumed, and the length of one arc obtained by dividing thecircumference of the circle by n (n is a natural number) is representedby λ, and the circumferential length of the circle is represented by nλ.A region of the piezoelectric ceramics corresponding to the regionforming each drive phase electrode is subjected to polarizationtreatment in advance by applying an electric field to the piezoelectricceramics in a thickness direction thereof alternately in an oppositedirection at a pitch of λ/2 along the circumferential direction.Therefore, when an electric field in the same direction is applied tothe piezoelectric ceramics in the thickness direction with respect toall the regions, the expansion and contraction polarity of thepiezoelectric ceramics in the regions is reversed alternately at a pitchof λ/2. The two regions forming the respective drive phase electrodesare arranged at a distance of an odd multiple of λ/4 in thecircumferential direction. In general, two regions (spacing regions)that separate the two drive phase electrodes from each other includenon-drive phase electrodes that are short-circuited to a commonelectrode so that piezoelectric vibration is not caused spontaneously,with the result that an electric field is not applied to thepiezoelectric ceramics in those regions. In general, a detection phaseelectrode is arranged in the spacing region as described later.

When an alternating voltage is applied to only one of the drive phaseelectrodes of such an ultrasonic motor, a first standing wave having awavelength λ is generated over the entire circumference of the vibrator.When an alternating voltage is applied to only the other drive phaseelectrode, a second standing wave is generated similarly, but theposition of the wave is rotated and moved by λ/4 in the circumferentialdirection with respect to the first standing wave. Meanwhile, whenalternating voltages, which have the same frequency and a temporal phasedifference of π/2, are applied to the respective drive phase electrodes,a propagating wave (wave number along the annular ring: n andwavelength: λ) of bending vibration (vibration having an amplitudeperpendicular to the surface of the vibrator), which propagates in thecircumferential direction over the entire circumference, is generated inthe vibrator as a result of the synthesis of both the standing waves.

When the propagating wave of the bending vibration (hereinaftersometimes simply referred to as “bending vibration wave”) is generated,each point on the surface of the vibrating plate forming the vibratorundergoes an elliptical motion. Therefore, the moving member that isbrought into contact with the surface rotates due to friction force(drive force) in the circumferential direction from the vibrating plate.The rotation direction can be reversed by switching, between positiveand negative, a phase difference π/2 of the alternating voltage appliedto each drive phase electrode. Further, the rotation speed can becontrolled by changing the frequency and amplitude of the alternatingvoltage applied to each drive phase electrode.

The generated bending vibration wave can be detected with the detectionphase electrode arranged in the spacing region. That is, the distortionof deformation (vibration) generated in the piezoelectric ceramicsbrought into contact with the detection phase electrode is convertedinto an electric signal in accordance with the magnitude of thedistortion and output to a drive circuit through the detection phaseelectrode.

When an alternating voltage is applied to the ultrasonic motor at afrequency higher than a resonant frequency, the ultrasonic motor startsa rotation operation. When the frequency is brought close to theresonant frequency, the rotation is accelerated to reach a highestrotation speed at the resonant frequency. Thus, the ultrasonic motor isgenerally driven at a desired rotation speed by sweeping the frequencyfrom a frequency region higher than the resonant frequency to theresonant frequency.

Meanwhile, a lead zirconate titanate-based material to be used as amaterial for the piezoelectric ceramics contains a large amount of leadin an A-site of an ABO₃ perovskite type metal oxide. Accordingly, aneffect of a lead component on environments has been seen as a problem.In order to deal with this problem, piezoelectric ceramics using aperovskite type metal oxide that does not contain lead (lead content issmaller than 1,000 ppm) has been proposed.

In Japanese Patent No. 5344456, there is disclosed piezoelectricceramics in which piezoelectric characteristics are enhanced bysubstituting a part of an A-site of barium titanate with calcium (Ca)and substituting a part of a B-site thereof with zirconium (Zr). InJapanese Patent No. 5213135, there is disclosed piezoelectric ceramicscontaining (Na,K)NbO₃ as a main component, in which piezoelectriccharacteristics are enhanced through use of a boundary of a rhombohedralphase and a tetragonal phase.

In recent years, the function of moving a weight body, e.g., asuper-telephoto lens with an ultrasonic motor is becoming necessary.However, with the piezoelectric ceramics disclosed in Japanese PatentNos. 5344456 and 5213135, even when an attempt is made to move a bodywith a high load, e.g., a super-telephoto lens by manufacturing anultrasonic motor through use of a related-art vibrator, the rotationspeed of a sufficient ultrasonic motor cannot be obtained due to theshortage of torque.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-mentionedproblems, and it is an object of the present invention to provide anultrasonic motor configured to be rotated with sufficient torque evenwhen lead-free piezoelectric ceramics is used. It is also an object ofthe present invention to provide a drive control system and an opticalapparatus that use the ultrasonic motor, and a vibrator to be used inthe ultrasonic motor.

In order to solve the above-mentioned problems, according to oneembodiment of the present invention, there is provided an ultrasonicmotor, including: an annular vibrator; and an annular moving memberarranged so as to be brought into pressure-contact with the annularvibrator, in which the annular vibrator includes: an annular vibratingplate; and an annular piezoelectric element arranged on a first surfaceof the annular vibrating plate, the annular vibrating plate beingbrought into contact with the annular moving member on a second surfaceon a side opposite to the first surface, in which the annularpiezoelectric element includes: an annular piezoelectric ceramic piece;a common electrode arranged on a surface of the annular piezoelectricceramic piece opposed to the annular vibrating plate so as to besandwiched between the annular piezoelectric ceramic piece and theannular vibrating plate; and a plurality of electrodes arranged on asurface of the annular piezoelectric ceramic piece on a side opposite tothe surface on which the common electrode is arranged, in which theannular piezoelectric ceramic piece contains lead in a content of lessthan 1,000 ppm, in which the plurality of electrodes include two drivephase electrodes, one or more non-drive phase electrodes, and one ormore detection phase electrodes, in which the second surface of theannular vibrating plate includes groove regions extending radially in Xportions, and when an outer diameter of the annular vibrating plate isset to 2R in a unit of mm, the X is a natural number satisfying2R/0.85−5≦X≦2R/0.85+15 and the outer diameter 2R is 57 mm or more, inwhich a ratio between an average value L_(top) of a length in acircumferential direction on an outer diameter side of a wall regionthat separates the adjacent groove regions from each other and anaverage value L_(btm) of a length in a circumferential direction on anouter diameter side of the groove regions falls within a range of2.00≦L_(top)/L_(btm)≦2.86, and in which, when center depths of thegroove regions in the X portions are represented by D₁ to D_(X) in orderin the circumferential direction, the D₁ to the D_(X) change so as tofollow a curve obtained by superimposing one or more sine waves on oneanother, the groove regions reaching a local maximum in 12 or moreregions in the change of the center depth and the groove regionsreaching a local minimum in 12 or more regions in the change of thecenter depth, the groove regions reaching the local maximum and thegroove regions reaching the local minimum being prevented from beingadjacent to each other.

In order to solve the above-mentioned problems, according to oneembodiment of the present invention, there is provided a drive controlsystem, including at least the above-mentioned ultrasonic motor and adrive circuit electrically connected to the ultrasonic motor.

In order to solve the above-mentioned problems, according to oneembodiment of the present invention, there is provided an opticalapparatus, including at least the above-mentioned drive control systemand an optical element dynamically connected to the ultrasonic motor.

In order to solve the above-mentioned problems, according to oneembodiment of the present invention, there is provided an annularvibrator, including: an annular vibrating plate; and an annularpiezoelectric element arranged on a first surface of the annularvibrating plate, in which the annular piezoelectric element includes: anannular piezoelectric ceramic piece; a common electrode arranged on asurface of the annular piezoelectric ceramic piece opposed to theannular vibrating plate so as to be sandwiched between the annularpiezoelectric ceramic piece and the annular vibrating plate; and aplurality of electrodes arranged on a surface of the annularpiezoelectric ceramic piece on a side opposite to the surface on whichthe common electrode is arranged, in which the annular piezoelectricceramic piece contains lead in a content of less than 1,000 ppm, inwhich the plurality of electrodes include two drive phase electrodes,one or more non-drive phase electrodes, and one or more detection phaseelectrodes, in which a second surface of the annular vibrating plateincludes groove regions extending radially in X portions, and when anouter diameter of the annular vibrating plate is set to 2R in a unit ofmm, the X is a natural number satisfying 2R/0.85−5≦X≦2R/0.85+15 and theouter diameter 2R is 57 mm or more, in which a ratio between an averagevalue L_(top) of a length in a circumferential direction on an outerdiameter side of a wall region that separates the adjacent grooveregions and an average value L_(btm) of a length in a circumferentialdirection on an outer diameter side of the groove regions falls within arange of 2.00≦L_(top)/L_(btm)≦2.86, and in which, when center depths ofthe groove regions in the X portions are represented by D₁ to D_(X) inorder in the circumferential direction, the D₁ to the D_(X) change so asto follow a curve obtained by superimposing one or more sine waves onone another, the groove regions reaching a local maximum in 12 or moreregions in the change of the center depth and the groove regionsreaching a local minimum in 12 or more regions in the change of thecenter depth, the groove regions reaching the local maximum and thegroove regions reaching the local minimum being prevented from beingadjacent to each other.

According to the present invention, in the ultrasonic motor using thelead-free piezoelectric ceramics or the drive control system and theoptical apparatus that use the ultrasonic motor, a sufficient drivespeed can be exhibited even when a high load (for example, 500 gf·cm ormore) is applied.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are each a schematic view for illustrating anultrasonic motor according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view for illustrating a part of aconfiguration of the ultrasonic motor according to the embodiment of thepresent invention.

FIG. 3 is a schematic view for illustrating a relationship between acircumferential length and the wavelength of a vibration wave in anannular piezoelectric element to be used in the ultrasonic motor and avibrator of the present invention.

FIG. 4A and FIG. 4B are each a schematic view of the annularpiezoelectric element to be used in the ultrasonic motor and thevibrator according to an embodiment of the present invention.

FIG. 5 is a graph for showing a relationship between the number ofprotrusion regions and groove regions, and the outer diameter of anannular vibrating plate to be used in the ultrasonic motor and thevibrator of the present invention.

FIG. 6A, FIG. 6B, FIG. 6C, and FIG. 6D are each a schematic view forillustrating a method of measuring a length in a circumferentialdirection on an outer diameter side of the protrusion region and thegroove region of the annular vibrating plate to be used in theultrasonic motor and the vibrator of the present invention.

FIG. 7A, FIG. 7B, FIG. 7C, and FIG. 7D are each a graph forschematically showing a distribution of a center depth of the grooveregions of the vibrating plate of the ultrasonic motor and the vibratoraccording to the embodiment of the present invention.

FIG. 7E, FIG. 7F, FIG. 7G, and FIG. 7H are each a graph forschematically showing a distribution of a center depth of the grooveregions of the vibrating plate of the ultrasonic motor and the vibratoraccording to the embodiment of the present invention.

FIG. 8 is a schematic view for illustrating a drive control systemaccording to an embodiment of the present invention.

FIG. 9A and FIG. 9B are each a schematic view for illustrating anoptical apparatus according to an embodiment of the present invention.

FIG. 10 is a schematic view for illustrating an optical apparatusaccording to the embodiment of the present invention.

FIG. 11A and FIG. 11B are each a schematic step view for illustrating anexample of a manufacturing process of the annular vibrating plate to beused in the ultrasonic motor and the vibrator of the present invention.

FIG. 12A, FIG. 12B, FIG. 12C, FIG. 12D, and FIG. 12E are each aschematic step view for illustrating an example of a manufacturingprocess of the ultrasonic motor of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

Now, an ultrasonic motor, a drive control system, an optical apparatus,and a vibrator according to embodiments of the present invention forcarrying out the present invention are described.

(Ultrasonic Motor and Vibrator that can be Used in Ultrasonic Motor)

The ultrasonic motor of the present invention has the followingfeatures. The ultrasonic motor includes an annular vibrator and anannular moving member that is arranged so as to be brought intopressure-contact with the vibrator. The vibrator includes an annularvibrating plate and an annular piezoelectric element arranged on a firstsurface (one surface) of the vibrating plate, a second surface (surfaceon a side opposite to the first surface) of the vibrating plate beingbrought into contact with the moving member. The piezoelectric elementincludes an annular piezoelectric ceramic piece (formed in an integratedmanner without seams), a common electrode arranged on one surface (on asurface opposed to the vibrating plate) of the piezoelectric ceramicpiece, and a plurality of electrodes arranged on the other surface (on aside opposite to the surface on which the common electrode is arranged)of the piezoelectric ceramic piece. The piezoelectric ceramic piececontains lead in a content of less than 1,000 ppm. The plurality ofelectrodes include two drive phase electrodes, one or more non-drivephase electrodes, and one or more detection phase electrodes. A secondsurface of the annular vibrating plate includes groove regions extendingradially in X portions. At this time, X is a natural number satisfying2R/0.85−5≦X≦2R/0.85+15 (2R is the outer diameter of the vibrating plate;unit: mm), 2R is 57 mm or more, and a ratio between an average valueL_(top) of a length in a circumferential direction on an outer diameterside of a wall region that separates the adjacent groove regions fromeach other and an average value L_(btm) of a length in a circumferentialdirection on an outer diameter side of the groove regions falls within arange of 2.00≦L_(top)/L_(btm)≦2.86. When center depths of the grooveregions in the X portions are represented by D₁ to D_(X) in order in thecircumferential direction, the D₁ to the D_(X) change so as to follow acurve obtained by superimposing one or more sine waves on one another,the groove regions reaching a local maximum in 12 or more regions in thechange of the center depth and the groove regions reaching a localminimum in 12 or more regions in the change of the center depth, thegroove regions reaching the local maximum and the groove regionsreaching the local minimum being prevented from being adjacent to eachother.

The ultrasonic motor of the present invention can exhibit a sufficientdrive speed with high torque even in a high load by satisfying theabove-mentioned condition. The ultrasonic motor of the present inventioncan also remove unnecessary vibration waves that do not contribute todrive so as to be driven with satisfactory efficiency (efficiency of anoutput with respect to input power to the ultrasonic motor) whileexhibiting a sufficient drive speed with high torque.

(FIG. 1A and FIG. 1B, and FIG. 2)

The ultrasonic motor of the present invention includes an annularvibrator 1 and an annular moving member 2 arranged so as to be incontact with the vibrator 1.

FIG. 1A and FIG. 1B are each a schematic view for illustrating theultrasonic motor according to an embodiment of the present invention.FIG. 1A is a schematic perspective view of the ultrasonic motor whenviewed from an oblique direction, and FIG. 1B is a schematic plan viewof the ultrasonic motor when viewed from a side on which a plurality ofelectrodes (pattern electrodes) are arranged.

FIG. 2 is a schematic partial sectional view of a detailed configurationof the ultrasonic motor according to the embodiment of the presentinvention when viewed from a side direction. The side direction as usedherein refers to a position away from the annular ring in a radialdirection.

(Annular Shape)

In the present invention, as described above, the annular shape refersto a shape in which a disc having a predetermined thickness can beschematically regarded as a configuration that includes a circularthrough hole concentrically. The outer peripheral shapes of the disc andthe through hole are ideally true circular shapes, but include an ovalshape, an elliptical shape, and the like as long as the shape can beschematically regarded as an annular ring. The radius and diameter whenthe circular shape is not a true circular shape are determined assuminga true circle having the same area. A substantially annular shape, suchas a shape in which a part of an annular ring is chipped, a shape inwhich a part of an annular ring is cut, or a shape in which a part of anannular ring protrudes, is also included in the annular shape in thepresent invention as long as the substantially annular shape can besubstantially regarded as an annular shape. Thus, a substantiallyannular shape that is slightly deformed due to the variation inmanufacturing is also included in the annular shape in the presentinvention as long as the substantially annular shape can besubstantially regarded as an annular shape. The radius and diameter whenthe circular shape is a substantially annular shape are determinedassuming a true circle in which a defective region and an abnormalregion are corrected.

(Moving Member)

The annular moving member 2 is similarly brought into pressure-contactwith the annular vibrator 1 and rotates by the drive force caused by thevibration generated in a contact surface with respect to the vibrator 1.It is preferred that the contact surface of the moving member 2 withrespect to the vibrator 1 be flat (even). It is preferred that themoving member 2 be formed of an elastic body, and a material for themoving member 2 be a metal. For example, aluminum is used suitably asthe material for the moving member 2. The surface of the aluminum may besubjected to alumite (anodization) treatment.

(Vibrator)

As illustrated in FIG. 1A, the vibrator 1 includes an annular vibratingplate 101 and an annular piezoelectric element 102 arranged on a firstsurface of the vibrating plate 101 and is brought into contact with themoving member 2 on a second surface of the vibrating plate 101.

It is preferred that the moving member 2 be pressed against the secondsurface of the vibrating plate 101 by appropriate external force so thatthe transmission of the drive force from the vibrator 1 to the movingmember 2 becomes more satisfactory.

An outer diameter 2R (unit: mm) of the vibrating plate 101 is 57 mm ormore (2R≧57). When the outer diameter 2R is smaller than 57 mm, a regionof the through hole becomes smaller, and hence the advantage of theannular ring may not be obtained. It is not practically suitable thatthe outer diameter be small, for example, in the case of using theultrasonic motor of the present invention for the purpose of moving alens for a camera so that the area through which a light flux passesbecomes smaller.

There is no particular limitation on the upper limit of the outerdiameter 2R of the vibrating plate 101, but from the viewpoint thatunnecessary vibration waves that do not contribute to drive can besufficiently removed, it is preferred that a relationship: 2R≦90 mm besatisfied. It is more preferred that a relationship: 2R≦80 mm besatisfied. When the outer peripheral surface of the vibrating plate 101does not have a simple shape and has a plurality of outer diametersdepending on a measurement position, the maximum outer diameter is setto 2R.

There is no particular limitation on an inner diameter 2R_(in) (unit:mm) of the vibrating plate 101 as long as the inner diameter 2R_(in) issmaller than the outer diameter 2R, but it is preferred that arelationship: 2R-16≦2R_(in)≦2R−6 be satisfied. This requirement can beinterpreted as setting a length in a radial direction of the annularring of the vibrating plate 101 (hereinafter referred to as “width” ofthe annular ring) to 3 mm or more and 8 mm or less. When the width ofthe annular ring of the vibrating plate 101 is set to within theabove-mentioned range, sufficient drive force is generated during driveof the ultrasonic motor while the advantage of the annular shape isensured. When the inner diameter 2R_(in) is smaller than 2R−16, a regionof the through hole becomes smaller. Therefore, the advantage of theannular ring may not be obtained as described above. Meanwhile, when2R_(in) is larger than 2R−6, the width of the annular ring of thevibrating plate 101 becomes insufficient, and there is a risk in thatthe drive force generated during drive of the ultrasonic motor maybecome insufficient. The drive force is substantially proportional tothe piezoelectric constant, the Young's modulus, and the thickness ofthe annular ring. When the drive force increases, the moving member canbe rotated at high speed even when the load of the moving member islarge.

It is preferred that the first surface of the vibrating plate 101 beflat so that the transmission of vibration involved in the expansion andcontraction of the piezoelectric element 102 becomes more satisfactory.It is preferred that the center of the annular ring of the vibratingplate 101 be matched with the center of the annular ring of thepiezoelectric element 102 so that the transmission of vibration becomesmore satisfactory.

There is no particular limitation on a method of arranging thepiezoelectric element 102 on the first surface of the vibrating plate101, but it is preferred to cause the piezoelectric element 102 todirectly adhere to the first surface of the vibrating plate 101 so asnot to inhibit the transmission of vibration or to cause thepiezoelectric element 102 to adhere to the first surface of thevibrating plate 101 through intermediation of a highly-elastic material(not shown). When an adhesive layer (not shown) having a Young's modulusat room temperature (e.g., 20° C.) of 0.5 GPa or more, more preferably 1GPa or more is arranged as an example of the highly-elastic material,the transmission of vibration from the piezoelectric element 102 to thevibrating plate 101 becomes more satisfactory. Meanwhile, the upperlimit of the Young's modulus at room temperature of the adhesive layermay not be set particularly, but in order to sufficiently obtainadhesion strength of a resin after curing, the upper limit of theYoung's modulus is preferably 10 GPa or less. For example, an epoxyresin is suitably used as the adhesive layer. The Young's modulus atroom temperature of the adhesive layer can be calculated by JIS K6911“General test methods for thermosetting plastics” (1995).

The maximum thickness of the vibrating plate 101 is represented byT_(dia) (unit: mm). As the maximum thickness of the vibrating plate 101,a distance between the first surface of the vibrating plate 101 and atop surface of a protrusion region 1011 is generally taken. When thethickness of the vibrating plate 101 varies depending on the position,the maximum value is basically defined as the maximum thickness of thevibrating plate 101.

It is preferred that the maximum thickness T_(dia) be 4 mm or more and 6mm or less. When the maximum thickness T_(dia) is smaller than 4 mm, aneutral surface of elastic deformation (distortion) as the vibrator 1 isshifted to a piezoelectric ceramic piece 1021 side, and hence theefficiency of motor drive is degraded. When the piezoelectric ceramicpiece 1021 is decreased in thickness for the purpose of returning theneutral surface to the vibrating plate 101 side, a stress duringdeformation increases in proportion to an inverse square of thethickness, and hence the piezoelectric ceramic piece 1021 is liable tocrack. Further, the generation force of the vibrator 1 decreases.Meanwhile, when the maximum thickness T_(dia) is larger than 6 mm, thedeformation amount during motor drive of the vibrating plate 101 becomessmaller, and the rotation speed of the motor decreases. When thepiezoelectric ceramic piece 1021 is increased in thickness for thepurpose of compensating for the deformation amount during motor drive ofthe vibrating plate 101, the drive voltage of the motor increasesexcessively.

(Material for Vibrating Plate)

It is preferred that the vibrating plate 101 be formed of an elasticbody for the purpose of forming a propagating wave of bending vibrationtogether with the piezoelectric element 102 and transmitting thevibration to the moving member 2. It is preferred that the vibratingplate 101 be made of a metal from the viewpoint of the properties andprocessability of the elastic body. As the metal that can be used as thevibrating plate 101, there may be given aluminum, brass, a Fe—Ni 36%alloy, and stainless steel. Of those, stainless steel is preferably usedin the present invention because stainless steel can provide a highrotation speed in combination with the piezoelectric ceramic piece 1021having a Young's modulus at room temperature of 80 GPa or more and 125GPa or less. Stainless steel as used herein refers to an alloycontaining 50 mass % or more of steel and 10.5 mass % or more ofchromium. Of the stainless steel, martensite stainless steel ispreferred, and SUS420J2 is most preferred as a material for thevibrating plate 101.

(Piezoelectric Element)

As illustrated in FIG. 1A, the annular piezoelectric element 102includes the annular piezoelectric ceramic piece 1021, a commonelectrode 1022 arranged on a surface of the piezoelectric ceramic piece1021 opposed to the vibrating plate 101, and a plurality of electrodes1023 arranged on a surface of the vibrating plate 101 on a side oppositeto the surface on which the common electrode 1022 is arranged.

In the present invention, the piezoelectric ceramic piece 1021 is a bulkhaving a uniform composition, which is obtained by calcining rawmaterial powder including metal elements, and refers to ceramics havingan absolute value of a piezoelectric constant d₃₁ at room temperature of10 pm/V or a piezoelectric constant d₃₃ at room temperature of 30 pC/Nor more. The piezoelectric constant of piezoelectric ceramics can bedetermined by calculation based on the Japan Electronics and InformationTechnology Industries Association Standard (JEITA EM-4501) from themeasurement results of a density, a resonant frequency, and anantiresonant frequency of the piezoelectric ceramics. This method ishereinafter referred to as a resonance-antiresonance method. The densitycan be measured, for example, by an Archimedes' method. The resonantfrequency and the antiresonant frequency can be measured, for example,through use of an impedance analyzer.

Ceramics is generally an aggregate of fine crystals (also called“polycrystal”), and each crystal includes an atom having a positivecharge and an atom having a negative charge. Most of the ceramics have astate in which the positive charge and the negative charge are balanced.However, dielectric ceramics also includes ceramics calledferroelectrics in which the positive charge and the negative charge incrystals are not balanced even in a natural state, and bias of charge(spontaneous polarization) occurs. The ferroelectric ceramics aftercalcination has spontaneous polarization in various directions and doesnot appear to have bias of charge in the entire ceramics. However, whena high voltage is applied to the ferroelectric ceramics, the directionsof spontaneous polarization are aligned in a uniform direction, and thespontaneous polarization does not return to the original directions evenwhen the voltage is removed. Aligning the directions of spontaneouspolarization is generally called polarization treatment. When a voltageis applied to the ferroelectric ceramics subjected to the polarizationtreatment from outside, the centers of the respective positive andnegative charges in the ceramics attract or repel external charge, andthe ceramics main body expands or contracts (inverse piezoelectriceffect). The piezoelectric ceramic piece 1021 of the present inventionis subjected to such polarization treatment to cause the inversepiezoelectric effect, and at least a region of a part of thepiezoelectric material piece is subjected to polarization treatment.

It is preferred that the outer diameter of the annular piezoelectricceramic piece 1021 be smaller than the outer diameter 2R of thevibrating plate 101, and the inner diameter of the annular piezoelectricceramic piece 1021 be larger than the inner diameter 2R_(in) of thevibrating plate 101. That is, it is preferred that, when the centers ofthe annular rings are matched, a projection surface of the piezoelectricceramic piece 1021 in an annular ring center axial direction be includedin a projection surface of the vibrating plate 101 in the samedirection. When the outer diameter and the inner diameter of the annularpiezoelectric ceramic piece 1021 are set to within such range, thetransmission of vibration between the piezoelectric ceramic piece 1021and the vibrating plate 101 becomes more satisfactory.

In the present invention, the piezoelectric ceramic piece 1021 containslead in a content of less than 1,000 ppm. That is, the piezoelectricceramic piece 1021 is lead-free piezoelectric ceramics. It is preferredthat the piezoelectric ceramic piece 1021 have a Young's modulus at roomtemperature (e.g., 20° C.) of 80 GPa or more and 125 GPa or less. TheYoung's modulus at room temperature of the piezoelectric ceramic piece1021 can be calculated by the above-mentioned resonance-antiresonancemethod. Most of the related-art piezoelectric ceramics contain leadzirconate titanate as a main component. Therefore, the following hasbeen indicated. For example, when a piezoelectric element is discardedand exposed to acid rain or left in a severe environment, there is arisk in that a lead component in the related-art piezoelectric ceramicsdissolves into the soil to cause harm to the ecosystem. However, whenthe content of lead is smaller than 1,000 ppm as in the piezoelectricceramic piece 1021 of the present invention, for example, even when apiezoelectric element is discarded and exposed to acid rain or left in asevere environment, the influence of the lead component contained in thepiezoelectric ceramic piece 1021 on the environment is negligible.

The content of lead contained in the piezoelectric ceramic piece 1021can be evaluated based on the content of lead with respect to the totalweight of the piezoelectric ceramic piece 1021, for example, quantifiedby X-ray fluorescence (XRF) analysis and ICP emission spectroscopicanalysis.

When the Young's modulus at room temperature of the piezoelectricceramic piece 1021 is smaller than 80 GPa, the drive force generatedduring drive of the ultrasonic motor may become insufficient. Meanwhile,when the Young's modulus at room temperature of the piezoelectricceramics 1021 is larger than 125 GPa, the piezoelectric ceramic piece1021 is liable to crack. For example, when the Young's modulus of thepiezoelectric ceramic piece 1021 is large, the stress caused bydeformation (distortion) of the piezoelectric ceramic piece 1021occurring due to the drive of the ultrasonic motor increases, and hencethere is a risk in that the piezoelectric ceramic piece 1021 is liableto crack. For example, when the Young's modulus is large, a neutralsurface of elastic deformation as the vibrator 1 is shifted from thevibrating plate 101 side to the piezoelectric ceramic piece 1021 side.Therefore, the efficiency of the motor drive is degraded. In view ofthis, when the thickness of the piezoelectric ceramic piece 1021 isreduced so as to return the neutral surface to the vibrating plate 101side, the stress during deformation increases in proportion to theinverse square of the thickness, and hence the piezoelectric ceramicpiece 1021 is liable to crack. The preferred range of the Young'smodulus at room temperature of the piezoelectric ceramic piece 1021 is95 GPa or more and 125 GPa or less.

As a main component of the piezoelectric ceramic piece 1021 in which thecontent of lead is smaller than 1,000 ppm, and the Young's modulus atroom temperature is GPa or more and 125 GPa or less, a metal oxide(perovskite type metal oxide) having a perovskite type crystal structureis preferred.

The perovskite type metal oxide of the present invention refers to ametal oxide having a perovskite structure that is ideally a cubicstructure as described in “Iwanami Dictionary of Physics and Chemistry”,Fifth Edition (Iwanami Shoten, published on Feb. 20, 1998). The metaloxide having a perovskite structure is generally represented by achemical formula of ABO₃. Although the molar ratio between the elementin the B-site and the O-element is described as 1:3, even when the ratioof the element amounts is slightly shifted (for example, from 1.00:2.94to 1.00:3.06), a metal oxide can be considered as a perovskite typemetal oxide as long as the metal oxide has a perovskite structure as amain phase. From structure analysis, for example, by X-ray diffractionor electron beam diffraction, it can be determined that the metal oxidehas a perovskite structure.

In the perovskite type metal oxide, elements A and B occupy specificpositions in the form of ions in a unit lattice, which are called A-siteand B-site. For example, in a cubic unit lattice, the element A ispositioned at a vertex of the cube while the element B occupies thebody-centered position of the cube. The element O occupies a face centerposition of the cube as an anion of oxygen. When the element A, theelement B, and the element O are respectively shifted slightly on thecoordinates from symmetric positions of the unit lattice, the unitlattice of the perovskite type structure is distorted to become atetragonal, rhombohedral, or orthorhombic crystal system.

As a combination of valences that can be taken by an A-site ion and aB-site ion, there are given A⁺B⁵⁺O²⁻ ₃, A²⁺B⁴⁺O²⁻ ₃, A³⁺B³⁺O²⁻ ₃, and asolid solution obtained by a combination thereof. The valence may be anaverage valance of a plurality of ions positioned in the same site.

There is no particular limitation on the composition of thepiezoelectric ceramic piece 1021 as long as the content of lead issmaller than 1,000 ppm (that is, lead-free). For example, piezoelectricceramics having a composition containing barium titanate, barium calciumtitanate, barium calcium zirconate titanate, bismuth sodium titanate,potassium sodium niobate, sodium barium titanate niobate, and bismuthferrite, and piezoelectric ceramics containing those compositions as amain component can be used in the ultrasonic motor and the vibrator 1 ofthe present invention.

Of those, it is preferred that the piezoelectric ceramic piece 1021contain a perovskite type metal oxide represented by one of thefollowing general formulae (1) and (2).

{M_(h)(Na_(j)Li_(k)K_(1-j-k))_(1-h)}_(1-m){(Ti_(1-u-v)Zr_(u)Hf_(v))_(h)(Nb_(1-w)Ta_(w))_(1-h)}O₃  (1)

(where M represents at least one kind selected from the group consistingof (Bi_(0.5)K_(0.5)), (Bi_(0.5)Na_(0.5)), (Bi_(0.5)Li_(0.5)), Ba, Sr,and Ca, and 0.06<h≦0.3, 0≦j≦1, 0≦k≦0.3, 0≦j+k≦1, 0<u≦1, 0≦v≦0.75,0≦w≦0.2, 0<u+v≦1, and −0.06≦m≦0.06.)

(Ba_(1-s)Ca_(s))_(α)(Ti_(1-t)Zr_(t))O₃ (0.986≦α≦1.100, 0.02≦s≦0.30, and0.020≦t≦0.095)  (2)

Further, it is preferred that the content of metal components other thanthe main component be 1 part by weight or less in terms of a metal withrespect to 100 parts by weight of the metal oxide represented by thegeneral formula.

In the general formulae (1) and (2), although the molar ratio betweenthe element in the B-site and the O-element is described as 1:3, evenwhen the ratio of the element amounts is slightly shifted (for example,from 1.00:2.94 to 1.00:3.06), the metal oxide falls within the scope ofthe present invention as long as the metal oxide has a perovskite typestructure as a main phase. From the structure analysis, for example, byX-ray diffraction or electron beam diffraction, it can be determinedthat the metal oxide has a perovskite type structure.

(Main Component and Other Metal Components)

In the present invention, the term “main component” means that thepiezoelectric ceramic piece 1021 contains 90 mass % or more of theperovskite type metal oxide represented by one of the general formulae(1) and (2) with respect to the total weight of the piezoelectricceramic piece 1021. The piezoelectric ceramic piece 1021 contains morepreferably 95 mass % or more, still more preferably 99 mass % or more ofthe perovskite type metal oxide.

In addition, it is preferred that the content of the metal componentsother than the main component be 1 part by weight or less in terms of ametal with respect to 100 parts by weight of the metal oxide representedby the general formula (1) or (2). The metal component refers to, forexample, typical metals, transition metals, rare-earth elements, andsemimetal elements such as Si, Ge, and Sb. The form of the metalcomponent contained in the piezoelectric ceramic piece 1021 is notlimited. For example, the metal component may be dissolved in solid inthe A-site or the B-site of the perovskite type structure or may becontained in a grain boundary. The metal component may also be containedin the piezoelectric ceramic piece 1021 in the form of a metal, an ion,an oxide, a metal salt, a complex, or the like.

When one or more metal elements selected from Mn, Cu, Fe, and Bi iscontained in the metal oxide represented by the general formula within arange of 1 part by weight or less in terms of a metal with respect to100 parts by weight of the metal oxide, an insulation property and amechanical quality factor of the piezoelectric ceramic piece 1021 areenhanced. Here, the mechanical quality factor refers to a factorrepresenting elasticity loss caused by vibration of the piezoelectricelement 102, and the magnitude of the mechanical quality factor isobserved as steepness of a resonance curve in impedance measurement.That is, the mechanical quality factor is a constant representing thesteepness of resonance of the piezoelectric element 102.

When the content of the metal component is more than 1 part by weight interms of a metal with respect to 100 parts by weight of the metal oxiderepresented by the general formula, there is a risk in that thepiezoelectric characteristics and insulation characteristics of thepiezoelectric ceramic piece 1021 may be degraded.

There is no particular limitation on a method of measuring a compositionof the piezoelectric ceramic piece 1021. As the method of measuring acomposition, there are given X-ray fluorescence analysis, ICP emissionspectroscopic analysis, and the like. The composition of the maincomponent and the contents of the other metal components contained inthe piezoelectric ceramic piece 1021 can be calculated by any of thosemethods.

(KNN-Based Piezoelectric Ceramics)

The general formula (1) represents a perovskite type metal oxide havingpiezoelectricity in which potassium sodium niobate (KNN) is used as abase material and Li, (Bi_(0.5)K_(0.5)), (Bi_(0.5)Na_(0.5)),(Bi_(0.5)Li_(0.5)), Ba, Sr, Ca, Ti, Zr, Hf, and Ta are subjected to sitesubstitution in an amount of at most 30 atomic % or less in order toadjust characteristics.

The Young's modulus at room temperature (for example, 20° C.) of thepiezoelectric ceramics containing the perovskite type metal oxiderepresented by the general formula (1) as a main component (hereinafterreferred to as “KNN-based piezoelectric ceramics) falls within a rangeof from about 80 GPa to about 125 GPa. In the piezoelectric ceramicsthat can be used in the present invention, the Young's modulus of theKNN-based piezoelectric ceramics falls within a low range. Therefore, inorder to obtain sufficient generation force during drive of theultrasonic motor, it is preferred that a relationship:2.00≦L_(top)/L_(btm)≦2.86 be satisfied. The more preferred range ofL_(top)/L_(btm) is 2.40≦L_(top)/L_(btm)≦2.86. When the average valuesL_(top) and L_(btm) satisfy the above-mentioned relationship, theultrasonic motor of the present invention using the KNN-basedpiezoelectric ceramics can transmit sufficient generation force whilehaving appropriate friction between the vibrator 1 and the moving member2.

The absolute value of the piezoelectric constant d₃₁ at room temperatureof the KNN-based piezoelectric ceramics 1021 is large at, for example,100 pm/V or more. Therefore, when the KNN-based piezoelectric ceramicsis used in the ultrasonic motor of the present invention, a highrotation speed is obtained during motor drive.

In the general formula (1), “h” representing the molar ratio of M, whichis a divalent or quasi divalent A-site metal, in the A-site falls withina range of 0.06≦h≦110.3. The abundance of Ti, Zr, and Hf, which arequadrivalent B-site metals, in the B-site is also introduced with themolar ratio h. With this, the charge balance (electrical neutrality) ofthe entire metal oxide is kept, and the insulation property of thepiezoelectric ceramic piece 1021 can be ensured.

The A-site of the KNN-based piezoelectric ceramics is originallymonovalent. However, when a part of the A-site is substituted with adivalent metal, a crystal structure changes, and the piezoelectricconstant can be enhanced. However, when “h” is larger than 0.3, there isa risk in that a depolarization temperature may decrease to, forexample, 100° C. or less.

The depolarization temperature (sometimes referred to as “T_(d)”) asused herein refers to temperature at which the piezoelectric constantdecreases as compared to that before the temperature is raised at a timewhen, after an elapse of a sufficient time period from polarizationtreatment, the temperature is raised from room temperature to thetemperature T_(d)(° C.) and lowered to room temperature again. Here, thetemperature at which the piezoelectric constant becomes less than 90% ofthat before the temperature is raised is referred to as thedepolarization temperature T_(d).

The B-site of the KNN-based piezoelectric ceramics is originallypentavalent. However, when a part of the B-site is substituted withquadrivalent Ti, Zr, or Hf, the transition temperature of a crystalstructure changes, and the change in piezoelectric constant with respectto the environmental temperature can be suppressed. The effect ofsuppressing the change in piezoelectric constant with respect to theenvironmental temperature decreases in the order of Zr, Ti, and Hf. When“v” representing the details of Hf in the quadrivalent metals is largerthan 0.75, the piezoelectric constant decreases, and there is a risk inthat the rotation speed of the piezoelectric motor may decrease.

In the A-site of the general formula (1), the alkali metals excludingthe above-mentioned “M” include Na, K, and Li. The total amount 1-h ofthe alkali metals in the A-site satisfies a relationship: 0.75≦1-h≦0.94.That is, a relationship: 0.06<h≦0.3 is satisfied. The bases of thealkali metals are Na and K, and the substitution amount k of Li is 0.3or less. When Li is substituted within the above-mentioned range withrespect to Na and K, there is an effect that the aspect ratio of alattice constant of a perovskite structure is enhanced to increase thedepolarization temperature.

In the general formula (1), “1-m” representing the molar ratio ofconstituent atoms in the A-site and the B-site of the perovskitestructure falls within a range of 0.945≦1-m≦1.06. That is, arelationship: −0.065≦m≦0.06 is satisfied. Ideally, a stoichiometricratio in which the number of constituent atoms in the A-site and thenumber of constituent atoms in the B-site have a ratio of 1:1, that is,a relationship: m=0 is preferred. However, in the actual step ofmanufacturing the KNN-based piezoelectric ceramics, “m” may changewithin a range of ±0.06. Within this range of “m”, the piezoelectricconstant of the KNN-based piezoelectric ceramics does not significantlychange.

A part of Nb in the B-site of the general formula (1) may be substitutedwith Ta, and the range of “w” representing the molar ratio ofsubstitution is 0≦w≦0.2. When Ta is substituted within the range of theabove-mentioned “w” with respect to Nb, the piezoelectric constant ofthe KNN-based piezoelectric ceramics is enhanced.

(BCTZ-Based Piezoelectric Ceramics)

The general formula (2) represents barium calcium zirconate titanate(BCTZ) obtained by substituting a part of Ba of barium titanate having aperovskite type structure with Ca and substituting a part of Ti thereofwith Zr. When Ca and Zr are simultaneously substituted, thepiezoelectric constant can be significantly enhanced without decreasingthe depolarization temperature of the piezoelectric ceramic piece 1021.It is preferred that the crystal system of the perovskite type metaloxide represented by the general formula (2) have a tetragonal structureat room temperature because a satisfactory mechanical quality factor canbe obtained.

The Young's modulus at room temperature (for example, 20° C.) of theBCTZ-based piezoelectric ceramic piece 1021 falls within a range of fromabout 80 GPa to about 125 GPa. In the piezoelectric ceramics that can beused in the present invention, the Young's modulus of the BCTZ-basedpiezoelectric ceramic piece 1021 falls within a high range, and hencethe high generation force can be obtained during drive of the ultrasonicmotor.

Meanwhile, the absolute value of the piezoelectric constant d₃₁ at roomtemperature of the BCTZ-based piezoelectric ceramic piece 1021 is largeat, for example, about 90 pm/V or more. Therefore, when the BCTZ-basedpiezoelectric ceramic piece 1021 is used in the ultrasonic motor of thepresent invention, a high rotation speed is obtained even in a high loadduring motor drive.

In the general formula (2), “α” representing the ratio between the molarquantity of Ba and Ca in the A-site and the molar quantity of Ti and Zrin the B-site fall within a range of 0.9865≦α≦1.100. When “α” is smallerthan 0.986, abnormal grain growth is liable to occur in crystal grainsforming the piezoelectric ceramic piece 1021, and the mechanicalstrength of the piezoelectric ceramic piece 1021 is degraded. Meanwhile,when “α” is larger than 1.100, the temperature required for grain growthof the piezoelectric ceramic piece 1021 becomes too high, with theresult that sintering cannot be performed in a general calcinationfurnace. Here, “sintering cannot be performed” refers to a state inwhich the density does not become a sufficient value and a great numberof pores and defects are present in the piezoelectric ceramic piece1021.

In the general formula (1), “s” representing the molar ratio of Ca inthe A-site falls within a range of 0.02≦s≦0.30. When a part of Ba ofperovskite type barium titanate is substituted with Ca within theabove-mentioned range, the phase transition temperature of anorthorhombic crystal system and a tetragonal crystal system is shiftedto a low temperature side, and hence stable piezoelectric vibration canbe obtained within the drive temperature range of the ultrasonic motorand the vibrator 1. However, when “s” is larger than 0.30, thepiezoelectric constant of the piezoelectric ceramic piece 1021 is notsufficient, and hence the rotation speed of the ultrasonic motor maybecome insufficient. Meanwhile, when “s” is smaller than 0.02, asufficient mechanical quality factor is not obtained within the drivetemperature range of the ultrasonic motor and the vibrator 1.

In the general formula (2), “t” representing the molar ratio of Zr inthe B-site falls within a range of 0.020≦t≦0.095. When a part of theTi-site is substituted with Zr within the above-mentioned range, thedistortion of a tetragonal crystal system of the piezoelectric materialis reduced, and hence c/a decreases to approach 1, with the result thatlarge piezoelectric vibration can be obtained. The more preferred rangeof “t” is 0.040≦t≦0.085. When “t” is larger than 0.095, thedepolarization temperature decreases, and there is a risk in that thedrive of the ultrasonic motor may not be sufficient in a hightemperature atmosphere, for example, at 50° C.

The common electrode 1022 is arranged on a surface of the annularpiezoelectric ceramic piece 1021 on a side opposed to the vibratingplate 101, that is, a surface that is brought into contact with thevibrating plate 101 or a surface that is brought into contact with theabove-mentioned adhesive layer. The common electrode 1022 is arranged inan annular manner similarly to the surface of the piezoelectric ceramicpiece 1021. It is preferred that the common electrode 1022 be broughtinto conduction with a non-drive phase electrode 10232 (see FIG. 1B)among the plurality of electrodes 1023 so that a drive voltage can beapplied to only a particular region of the plurality of electrodes 1023.For example, when wiring is arranged so as to be brought into contactwith both the common electrode 1022 and the non-drive phase electrode10232, both the common electrode 1022 and the non-drive phase electrode10232 can be brought into conduction. Alternatively, wiring may bearranged so as to bring the common electrode 1022 and the non-drivephase electrode 10232 into conduction through intermediation of thevibrating plate 101 having conductivity.

Such wiring can be formed, for example, by applying a metal paste madeof, for example, silver and drying or baking the metal paste.

As illustrated in FIG. 1B, the plurality of electrodes 1023 include twodrive phase electrodes 10231, one or more non-drive phase electrodes10232, and one or more detection phase electrodes 10233. It is preferredthat the drive phase electrodes 10231, the non-drive phase electrode10232, and the detection phase electrode 10233 not be brought intoconduction with each other so that each electrode can have anindependent potential during drive.

The detection phase electrode 10233 is arranged for the purpose ofdetecting a vibration state of the vibrator 1 and feeding backinformation on the vibration state to the outside, for example, a drivecircuit. The piezoelectric ceramic piece 1021 in a region that isbrought into contact with the detection phase electrode 10233 issubjected to polarization treatment. Therefore, when the ultrasonicmotor is driven, a voltage corresponding to the magnitude of deformation(distortion) of the vibrator 1 is generated in a region of the detectionphase electrode 10233 and output to the outside as a detection signal.

It is preferred that at least one non-drive phase electrode 10232 bebrought into conduction with the common electrode 1022 because thenon-drive phase electrode 10232 can be used as a ground electrode. Anexemplary mode and procedure for obtaining conduction are as describedabove. When the drive phase electrode 10231, the non-drive phaseelectrode 10232 serving as a ground electrode, and the detection phaseelectrode 10233 are arranged on one surface (surface opposite to asurface on which the common electrode 1022 is arranged) of the annularpiezoelectric element 102, the transmission of an electric signal (drivesignal, detection signal) with respect to the outside of the ultrasonicmotor is facilitated. For example, a drive signal and detectionvibration can be transmitted through a flexible printed board.

When a flexible printed board is used for electrical connection of theultrasonic motor and the drive circuit, the flexible printed board isarranged so as to be brought into contact with a part of each drivephase electrode 10231, the non-drive phase electrode 10232, and thedetection phase electrode 10233 on one surface of the annularpiezoelectric element 102 (surface on a side opposite to a surface whichthe common electrode 1022 faces). The flexible printed board has highdimension accuracy and can be positioned easily through use of a jig orthe like. For connection of the flexible printed board, thermal pressurebonding can also be performed through use of an epoxy adhesive or thelike. However, from the viewpoint of mass production, it is preferredthat an anisotropic conductive paste (ACP) and an anisotropic conductivefilm (ACF) that have conductivity be subjected to thermal pressurebonding so that a conduction failure can be reduced and a process speedis increased. When thermal pressure bonding is used for connection ofthe flexible printed board, it is preferred to select a temperaturelower than the depolarization temperature of the piezoelectric ceramicpiece 1021.

The piezoelectric ceramic piece 1021 in a region that is in contact withthe non-drive phase electrode 10232 may or may not have residual(remanent) polarization. When the piezoelectric ceramic piece 1021 in aregion that is brought into contact with the non-drive phase electrode10232 has residual polarization, it is preferred that the non-drivephase electrode 10232 and the common electrode 1022 be brought intoconduction with each other.

As illustrated in FIG. 1B, each drive phase electrode 10231 includes sixpolarizing electrodes 102311 and a connecting electrode 102312 thatelectrically connects the six polarizing electrodes 102311.

FIG. 3 is a schematic view for illustrating a relationship between thecircumferential length and the wavelength of a vibration wave in theannular piezoelectric element 102 to be used in the ultrasonic motor ofthe present invention. In FIG. 3, for convenience of description, theelectrodes are not shown. The annular ring in FIG. 3 represents thepiezoelectric element 102 and has substantially the same shape as thatof the piezoelectric ceramic piece 1021. When an arbitrary position isdesignated on a surface of the annular ring, and the diameter of acircle that passes through the arbitrary position and shares its centerwith the annular shape of the piezoelectric element 102 is representedby 2R_(arb) (unit: mm), the circumferential length of the circle is2πR_(arb). The circumferential length 2πR_(arb) is set to 7λ in thepresent invention. “λ” in the present invention refers to the wavelengthat a time when a propagating wave of 7th order (wave number: 7) bendingvibration is generated in the circumferential direction of the vibrator1 forming the ultrasonic motor of the present invention. The value of λvaries depending on the arbitrary position designated above, but suchparameter λ is assumed in order to design the shape and dimensions ofthe plurality of electrodes 1023. The circumferential length ishereinafter considered assuming the circle that passes through thearbitrary position on the surface of the piezoelectric element 102 evenwhen there is no particular description.

FIG. 4A and FIG. 4B are each a schematic view for illustrating thearrangement of the polarizing electrodes 102311 in the annularpiezoelectric element 102 to be used in the ultrasonic motor of thepresent invention and the polarity of the piezoelectric ceramic piece1021 in each electrode region, when the annular piezoelectric element102 is viewed from a side on which the plurality of electrodes arearranged. For convenience of description, in FIG. 4A and FIG. 4B, theconnecting electrode 102312 is not shown. A combination of thepolarities in FIG. 4A and FIG. 4B is an example and does not limit thepresent invention.

The piezoelectric ceramic piece 1021 in a region that is brought intocontact with the drive phase electrode 10231 has residual polarizationin a direction substantially perpendicular to the drive phase electrode10231. A region having residual polarization may be a part or a whole ofthe piezoelectric ceramic piece 1021 in a region held between thepolarizing electrodes 102311 and the common electrode 1022. From theviewpoint of enhancing the generation force during drive of theultrasonic motor, it is preferred that the entire region held betweenthe polarizing electrodes 102311 and the common electrode 1022 haveresidual polarization. In the present invention, the region havingresidual polarization is referred to as “polarized region”. The residualpolarization refers to polarization that remains in the piezoelectricceramic piece 1021 at a time when a voltage is not applied to thepiezoelectric ceramic piece 1021. When the piezoelectric ceramic piece1021 is subjected to polarization treatment, the direction ofspontaneous polarization is aligned in a voltage application direction,and thus the piezoelectric ceramic piece 1021 has residual polarization.Whether or not the piezoelectric ceramic piece 1021 has residualpolarization can be determined by applying voltage between theelectrodes holding the piezoelectric element 102 and measuring anapplied electric field E and a polarization amount P (P-E hysteresiscurve).

Each drive phase electrode 10231 includes the six polarizing electrodes102311, and correspondingly, there are six regions of the piezoelectricceramic piece 1021 that are brought into contact with the polarizingelectrodes 102311, that is, six polarized regions. The six polarizedregions and the six polarizing electrodes 102311 are arranged along thecircumference so as to sandwich unpolarized regions therebetween asillustrated in FIG. 4A and FIG. 4B. The polarities of the polarizedregions are reversed alternately in order of the arrangement along thecircumference. In FIG. 4A and FIG. 4B, symbols “+” and “−” written on aninner side of the polarizing electrodes 102311 represent directions ofresidual polarization, that is, polarities. In this specification, thesymbol “+” is written in the electrode region to which a positivevoltage is applied in the polarization treatment in the manufacturingstep of the piezoelectric element 102. Therefore, when the piezoelectricconstant d₃₃ is measured only in the “+” electrode region, a negativevalue is detected. Similarly, in the “−” electrode region, a positivepiezoelectric constant d₃₃ is detected. Meanwhile, only in the electroderegions having the symbol “0” written in FIG. 4B or the unpolarizedregions having no electrodes arranged in FIG. 4B, only the piezoelectricconstant d₃₃ at room temperature of zero or an extremely small value,e.g., 5 pC/N or less is detected. In the piezoelectric element 102illustrated in FIG. 4A and FIG. 4B, the piezoelectric ceramic piece 1021includes a region having downward residual polarization and a regionhaving upward residual polarization with respect to the drawing sheet.As a method of confirming that the polarity of residual polarizationvaries depending on the region, there are a method involving determiningthe variation in polarity based on the plus and minus of a valuedetected by measuring a piezoelectric constant and a method involvingconfirming that a shift direction from an original point of a coerciveelectric field in a P-E hysteresis curve is opposite.

Each polarized region and each polarizing electrode 102311 hassubstantially the same dimensions.

Specifically, it is preferred that the six polarizing electrodes 102311(12 polarizing electrodes 102311 as a total of the two drive phaseelectrodes 10231) have an equal length in the circumferential direction.It is also preferred that each polarized region and each polarizingelectrode 102311 have a difference of less than 2% in terms of aprojection area.

More specifically, each polarizing electrode 102311 has a fan shape, andthe length thereof in the circumferential direction is ideally λ/2 whenthe unpolarized regions are ignored. Actually, in order to preventshort-circuiting at a time when adjacent regions create polarized stateshaving different polarities, the unpolarized regions are present betweenthe respective polarizing electrodes 102311. In this case, it is idealthat the center of the unpolarized region in the circumferentialdirection be taken as a starting point, and a distance from the startingpoint to the center of the subsequent unpolarized region beyond theadjacent polarizing electrode 102311 be set to λ/2. However, an error oflength of about less than 2% is allowed. From the viewpoint of enhancingdrive force generated during drive of the ultrasonic motor, it ispreferred that the volume of the unpolarized regions be as small aspossible. The unpolarized regions sandwiched between the polarizingelectrodes 102311 are brought into contact with the connecting electrode102312.

The length of each drive phase electrode 10231 in the circumferentialdirection is ideally 3λ. Actually, there is a gap having no electrode inorder to prevent short-circuiting with respect to the adjacent non-drivephase electrode 10232 or the detection phase electrode 10233, and hencethe length is slightly smaller than 3λ. Actually, the length is set tobe, for example, smaller than 3λ by from about 1% to about 2.5%.

The circumferential length of the circle that passes through anarbitrary position on the surface of the piezoelectric element 102 is7λ, and hence a residual region of the circumferential length excludingthe two drive phase electrodes 10231 is λ when the gap between theelectrodes is ignored. The residual region is shared by one or morenon-drive phase electrodes 10232 and one or more detection phaseelectrodes 10233. In this case, the two drive phase electrodes 10231need to be separated from each other in the circumferential direction bytwo spacing regions having circumferential lengths of λ/4 and 3λ/4,respectively. The non-drive phase electrode 10232 and the detectionphase electrode 10233 need to be arranged in two spacing regions. Withthis, phases of standing waves generated in regions of the two drivephase electrodes 10231, for example, the positions of nodes are shiftedby λ/4, and the annular piezoelectric element 102 including thepolarized regions having different polarities can form a bendingvibration wave in the circumferential direction of the vibrator 1. Thisis because, when a voltage is applied simultaneously to each polarizingelectrode 102311 through the connecting electrode 102312, one of thepolarized regions expands and the other contracts in the circumferentialdirection due to the inverse piezoelectric effect.

When an alternating voltage having a frequency serving as a naturalfrequency of the vibrator 1 is applied to only a region sandwichedbetween one drive phase (phase A) electrode 10231 and the commonelectrode 1022 of the ultrasonic motor of the present invention, astanding wave having a wavelength λ is generated over the entirecircumference along the circumferential direction on the surface of thevibrating plate 101. When an alternating voltage is similarly applied toonly a region sandwiched between the other drive phase (phase B)electrode 10231 and the common electrode 1022, a similar standing waveis generated. The positions of nodes of the respective standing waveshave a shift of λ/4 along the circumferential direction of the vibratingplate 101.

When the ultrasonic motor is driven, an alternating voltage having afrequency serving as a natural frequency of the vibrator 1 is applied toregions of the two drive phase (phase A and phase B) electrodes 10231 ofthe ultrasonic motor of the present invention so that the frequency isthe same and a temporal phase difference becomes π/2. With this, due tothe synthesis of the two standing waves, a 7th order propagating wavehaving the wavelength λ, which propagates in the circumferentialdirection, is generated in the vibrating plate 101.

The polarizing electrode 102311, the non-drive phase electrode 10232,the detection phase electrode 10233, and the connecting electrode 102312are formed of a layer-like or film-like conductor having a resistance ofless than 10Ω, preferably less than 1Ω. The resistance of the electrodescan be evaluated, for example, by measuring a resistance with a circuittester (electric tester). The thickness of each electrode is from about5 nm to about 20 μm. There is no particular limitation on the materialfor each electrode, and any material that is generally used in apiezoelectric element may be used.

As the material for the electrodes, there are given, for example, metalssuch as Ti, Pt, Ta, Ir, Sr, In, Sn, Au, Al, Fe, Cr, Ni, Pd, Ag, and Cu,and compounds thereof. The electrodes may be formed of one kind of theabove-mentioned examples or laminations of two or more kinds thereof.The respective electrodes arranged in the piezoelectric element may bemade of different materials.

Of those, as the electrode to be used in the present invention, an Agpaste or Ag baked electrode, an Au/Ti sputtered electrode, or the likeis preferred because a resistance is low.

(Vibrating Plate)

As illustrated in FIG. 2, the second surface of the vibrating plate 101that is brought into contact with the moving member 2 includes aplurality of groove regions 1012, each having a U-shaped cross-section,which extend radially. The “U-shaped cross-section” as used hereinrefers to a sectional shape having both wall surfaces substantiallyperpendicular to the second surface of the vibrating plate 101 and abottom surface substantially horizontal thereto. The U-shapedcross-section widely includes not only a so-called U-shape in which abottom surface and each wall surface are smoothly connected to eachother in a rounded manner, but also a shape similar to the so-calledU-shape, which can be regarded as the “U-shaped cross-section”, such asa so-called rectangular shape in which a bottom surface and each wallsurface are connected to each other so as to form a right angle, anintermediate shape thereof, or a shape slightly deformed from thoseshapes. FIG. 6B, FIG. 6C, and FIG. 6D are each an illustration of anexemplary sectional shape of a groove region having a U-shapedcross-section included in the present invention.

The second surface of the vibrating plate 101 includes the plurality ofgroove regions 1012 that are arranged radially, and hence a regionbetween two adjacent groove regions forms a wall region 1011 thatseparates the two groove regions from each other. The plurality ofgroove regions 1012 extending radially are arranged in thecircumferential direction, and hence the number of the wall regions 1011formed therebetween is the same as that of the groove regions 1012. Atop surface (ceiling surface) of the wall region 1011 corresponds to thesecond surface of the annular vibrating plate 101 and also serves as areference surface for defining a depth of each groove region 1012.However, the wall region 1011 can be regarded as a convex region withrespect to the groove region 1012 that is a concave region, and hencethe wall region can also be referred to as “protrusion region”. That is,the moving member 2 can relatively move with respect to the vibrator 1,with which the moving member 2 is brought into pressure-contact, withdrive force caused by friction with respect to the top surface of theprotrusion region 1011. In the following, for convenience ofdescription, the region 1011 between the groove regions 1012 is referredto as “protrusion region” instead of “wall region” in principle.

The groove regions 1012 of the present invention have a feature in thatthe center depth varies depending on each groove region 1012 (in FIG. 2,the center depth is shown as the same center depth). The “center depth”as used herein refers to a depth at a center position at a time wheneach groove region 1012 is viewed from the moving member 2 side. Thatis, the center depth refers to a depth of a groove measured from a topsurface (second surface of the vibrating plate 101) of the protrusionregion at a position corresponding to the center of each groove regionboth in the radial direction and the circumferential direction. Ingeneral, the bottom surface of the groove region 1012 is parallel as awhole to the second surface of the vibrating plate 101, is flat as awhole in the radial direction (direction in which the groove extends),and is flat as a whole in the circumferential direction (direction inwhich the grooves are arranged), or has a concave surface shape in whichthe center portion is flat and both side portions (vicinity of the wallsurface) are raised. Therefore, the center depth means a depth of thedeepest portion of each groove region. However, the foregoing variesdepending on the bottom surface shape of each groove region, and hencethe center depth does not necessarily always refer to the depth of thedeepest portion. For example, the center depth may refer to a medianvalue of a depth (for example, when the bottom surface is inclined inone direction). When the depth at the center position is a value thatdoes not generally have a meaning as a representative value of a depthof the groove region (for example, a significant point), a valuerepresenting the depth of the groove region, which is a depth at anotherpoint close to the center position, is defined as a center depth. When ameasurement position of a depth is fixed in all the groove regions, andthe bottom surface of each groove region has the same shape, thesignificance of the center depth is the same in all the groove regions.

The protrusion regions (wall regions) 1011 and the groove regions 1012are alternately arranged along the circumferential direction of theannular vibrating plate 101, and as described above, the number of theprotrusion regions 1011 is the same as that of the groove regions 1012.It is assumed that the protrusion regions 1011 and the groove regions1012 are each present in X portions. The number of the protrusionregions 1011 or the groove regions 1012 is determined so as to besubstantially proportional to the outer diameter 2R of the vibratingplate 101, and so as to satisfy a relationship: 2R/0.85−5≦X≦2R/0.85+15.Here, the unit of 2R is mm, and the unit of X is a portion (number).When X and 2R satisfy the above-mentioned relationship, the ultrasonicmotor of the present invention can transmit sufficient drive force whilehaving appropriate friction between the vibrator 1 and the moving member2.

FIG. 5 is a graph for showing a relationship between the number of thegroove regions 1012 (or the protrusion regions 1011) of the vibratingplate 101 and the outer diameter 2R of the vibrating plate 101. Acolored region including the line segments of FIG. 5 falls within thescope of the present invention. It is not particularly necessary toprovide an upper limit to the outer diameter 2R, but the description ofthe range in which the outer diameter 2R is more than 90 mm is notshown.

Meanwhile, the outer diameter 2R of the vibrating plate 101 is set to 57mm or more, and hence a minimum value of the number X of the grooveregions 1012 is 63. When the upper limit of the outer diameter 2R is 90mm, a maximum value of the number X is 120. As another example, when theupper limit of the outer diameter 2R is 80 mm, the maximum value of thenumber X is 109.

When the number X of the groove regions 1012 is a natural number smallerthan 2R/0.85−5, the deformation (distortion) of the protrusion regions1011 that are brought into contact with the moving member 2 becomesinsufficient, and as a result, the drive force generated by the vibrator1 decreases. Meanwhile, when the number X is a natural number largerthan 2R/0.85+15, the contact area with the moving member 2 for oneprotrusion region 1011 decreases. Therefore, when a weight body is usedas an element on the moving member 2 side or large torque is applied tothe moving member 2, the friction force between the moving member 2 andthe protrusion regions 1011 becomes insufficient, and the drive force isnot sufficiently transmitted, with the result that sliding may occur.

From the viewpoint of the generation force during motor drive and theprevention of sliding, the range of the number X is more preferably85≦X≦100.

FIG. 6A to FIG. 6D are each a schematic view for illustrating a methodof measuring lengths (unit: mm) in the circumferential direction (on theouter diameter side) of the protrusion region 1011 and the groove region1012 of the annular vibrating plate 101 to be used in the ultrasonicmotor of the present invention or the vibrator 1 of the presentinvention. When a boundary line between the protrusion region 1011 andthe groove region 1012 extends accurately in the radial direction (thatis, the groove region 1012 is formed in a fan shape), the ratio of thelengths thereof in the circumferential direction is the same even whenthe circumference is taken at any position on the surface of thevibrating plate 101. However, in general, the groove region 1012 doesnot have a fan shape and is formed into a shape in which the center lineof the groove extends in the radial direction, and both wall surfacesextend in parallel to the center line (rectangular shape when viewedfrom the moving member 2 side). Thus, in a strict sense, the ratio ofthe lengths of the protrusion region 1011 and the groove region 1012 inthe circumferential direction slightly varies depending on where thecircumference is taken (radius of the virtual circle). In such case, thecircumference is taken on the outer diameter side of the vibrating plate101, and the radius of the virtual circle is set to R.

In the present invention, a ratio between an average value L_(top) oflengths of the protrusion regions 1011 in the circumferential directionon the outer diameter side and an average value L_(btm) of lengths ofthe groove regions 1012 in the circumferential direction on the outerdiameter side is 2.00≦L_(top)/L_(btm)≦2.86. When the average valuesL_(top) and L_(btm) satisfy the above-mentioned relationship, theultrasonic motor of the present invention can sufficiently transmit thedrive force generated in the vibrator 1 while having appropriatefriction force between the vibrator 1 and the moving member 2.

FIG. 6A is a schematic partial plan view of the vibrating plate 101 whenviewed from a side of a surface (second surface) that is brought intocontact with the moving member 2. It is assumed that one arbitraryprotrusion region is selected from the protrusion regions (1011-1 to1011-X) in X portions. The length (arc) of the selected protrusionregion 1011-1 in the circumferential direction on the outer diameterside is represented by L_(top1). Lengths of the other protrusion regions1011-2 to 1011-X in the circumferential direction on the outer diameterside are similarly determined, and an average of the lengths (L_(top1)to L_(topX)) in the X portions is determined to be the average valueL_(top). An average is taken, and hence the lengths of the protrusionregions 1011 in the circumferential direction on the outer diameter sidemay be equal to or different from each other.

Similarly, one arbitrary groove region is selected from the grooveregions (1012-1 to 1012-X) in the X portions. The length (arc) of theselected groove region 1012-1 in the circumferential direction on theouter diameter side is represented by L_(btm1). The lengths of the othergroove regions 1012-2 to 1012-X in the circumferential direction on theouter diameter side are similarly determined, and an average of thelengths (L_(btm1) to L_(btmX)) in the X portions is determined to be theaverage value L_(btm). An average is taken, and hence the lengths of thegroove regions 1012-1 to 1012-X in the circumferential direction on theouter diameter side may be equal to or different from each other.

FIG. 6B, FIG. 6C, and FIG. 6D are each a schematic developed view of apart of the vibrating plate 101 including the arbitrary protrusionregion 1011-1 and the arbitrary groove region 1012-1 when viewed fromthe outer diameter side of the annular ring (position away from theannular ring in the radial direction). When the protrusion region 1011-1and the groove region 1012-1 are formed into a rectangular shape or asubstantially rectangular shape as illustrated in FIG. 6B, it is onlynecessary that the length of a ceiling side of the protrusion region(top surface on the outer diameter side) be set to the length L_(top1),and the length of a bottom side of the groove region (bottom surface onthe outer diameter side) be set to the length L_(btm1).

When a wall surface common to the protrusion region 1011-1 and thegroove region 1012-1 is perpendicular to the first surface of thevibrating plate 101, but the top surface of the protrusion region 1011-1or the bottom surface of the groove region 1012-1 is not flat asillustrated in FIG. 6C, the lengths L_(top1) and L_(btm1) can bedetermined based on the distance between the wall surfaces on the outerdiameter side. When the wall surface common to the protrusion region1011-1 and the groove region 1012-1 is not perpendicular to the firstsurface of the vibrating plate 101 as illustrated in FIG. 6D, aperpendicular line to the first surface of the vibrating plate 101 isassumed at a position on the wall surface serving as an intermediateposition between the center height of the protrusion region 1011-1 andthe center depth of the groove region 1012-1, and this position may beused as a reference when measuring the lengths L_(top1) and L_(btm1).

When the ratio L_(top)/L_(btm) of the lengths of the protrusion region1011 and the groove region 1012 in the circumferential direction on theouter diameter side is smaller than 2.00, the contact area of theprotrusion regions 1011 in the X portions with respect to the movingmember 2 decreases. Therefore, when a weight body is used as an elementon the moving member 2 side or large torque (for example, 500 gf·cm ormore) is applied to the moving member 2, the friction force between themoving member 2 and the protrusion regions 1011 becomes insufficient,and the drive force is not effectively transmitted to cause sliding,with the result that a drive speed may decrease. Meanwhile, when theratio L_(top)/L_(btm) is larger than 2.86, the deformation (distortion)of the protrusion regions 1011 that are brought into contact with themoving member 2 becomes insufficient, with the result that the driveforce generated by the vibrator 1 decreases, and hence the drive speeddecreases.

The ratio L_(top)/L_(btm) is more preferably 2.00≦L_(top)/L_(btm)≦2.40.

In any of the cases of FIG. 6B, FIG. 6C, and FIG. 6D, further includingcases not shown in those figures, from the viewpoint of increasing thecontact with the moving member 2, it is preferred that the distancesfrom the first surface of the vibrating plate 101, which serves as astarting point, to the maximum points of the protrusion regions 1011-1to 1011-X be equal to each other within a range of tolerance ofprocessing dimensions.

Center depths of the groove regions 1012 in the X portions arerespectively represented by D₁ to D_(X) (unit: mm) in order of thecircumferential direction of the vibrating plate 101. In the presentinvention, the center depths D₁ to D_(X) take five kinds or more ofdifferent values and change so as to follow a curve obtained bysuperimposing one or more sine waves on one another.

For example, in the case of suppressing 4th order, 5th order, 6th order,and 8th order (wave number along the annular ring is 4, 5, 6, and 8)propagating waves, which serve as the unnecessary vibration waves withrespect to the 7th order propagating wave along the annular ringintended by the present invention, it is only necessary that the centerdepths D₁ to D_(X) are changed along the curve obtained by superimposingone or more and four or less sine waves on one another. A generalformula of the curve obtained by superimposing sine waves on one anotherin that case is represented by the following expression (1).

D=D _(ave) +Am ₄×sin(4×2×ω+θ₄)+Am ₅×sin(5×2×ω+θ₅)+Am ₆×sin(6×2×ω+θ₆)+Am₈×sin(8×2×ω+θ₈)  Expression 1

In the expression (1), ω represents an angle indicating a centerposition of a groove of the annular vibrating plate 101 extendingradially. θ represents an angle indicating a phase difference and isappropriately determined so as to satisfy conditions described later inthe embodiment. D (unit: mm) represents a depth of an ideal groove at acenter position of an arbitrary groove of the annular vibrating plate101, and the center depths D₁ to D_(X) are set to D±0.1. The depthchange of the respective values of the center depths D₁ to D_(X) ismatched with D calculated by the expression (1). D_(ave) (unit: mm)represents a standard depth of the groove region 1012 that is setseparately as an average value of the center depths D₁ to D_(X).

Am (unit: mm) is a real number to be an amplitude of each sine wave, anda suffix represents an order (wave number) of the unnecessary vibrationwaves intended to be reduced. Of Am₄, Am₅, Am₆, and Am₈, at least onetakes a value other than 0. The number of amplitudes having values otherthan 0 is the number of sine waves to be superimposed on one another.There is no particular limitation on an upper limit thereof as long asthe number of sine waves to be superimposed on one another is one ormore. However, when five or more sine waves are superimposed on oneanother, the effect of reducing the unnecessary vibration waves is notsubstantially enhanced, and there is a risk in that the efficiency ofmotor drive may be degraded. Thus, it is preferred that the number ofsine waves to be superimposed on one another be one or more and four orless. The more preferred number of sine waves to be superimposed on oneanother is two or more and four or less.

FIG. 7A, FIG. 7B, FIG. 7C and FIG. 7D, and FIG. 7E, FIG. 7F, FIG. 7G,and FIG. 7H are each a graph for schematically showing a distribution ofa center depth of the groove regions of the vibrating plate of theultrasonic motor according to the embodiment of the present invention.FIG. 7A and FIG. 7C, and FIG. 7E and FIG. 7G are each an example forshowing a difference between the center depth and the standard depthD_(ave) of each groove region at a time when it is assumed that X is 90.A horizontal axis of each plot represents the order of 90 groove regions(hereinafter referred to as “groove number”). The 0th groove region doesnot actually exist, but is used for convenience on the plot so as toshow the depth of the 90th groove region twice. The plots of a depth ofeach groove region in FIG. 7A and FIG. 7C, and FIG. 7E and FIG. 7Gfollow a curve obtained by superimposing four sine waves on one anotherin both cases.

FIG. 7B, FIG. 7D, and FIG. 7H are each a graph for schematicallyshowing, as a graph plot, a relationship of the height of the protrusionregion and the depth of the groove region in the case of application tothe vibrating plate 101, with the center depth of each groove regionshown in each of FIG. 7A, FIG. 7C, and FIG. 7G being the standard depthD_(ave) of 1.85 mm. In this example, the heights of the respectiveprotrusion regions, with the first surface of the vibrating plate 101being a starting point, are equal to each other. The horizontal axis ofeach plot represents positions of the 90 groove regions as angles whenviewed from the center of the annular ring. The values on the horizontalaxis are relative values, but in FIG. 7B, the center of the protrusionregion sandwiched between the 89th groove region and the 90th (0th)groove region in FIG. 7A is set to a starting point.

Similarly, FIG. 7F is a graph for schematically showing, as a graphplot, a relationship of the height of the protrusion region and thedepth of the groove region in the case of application to the vibratingplate 101, with the center depth of each groove region shown in FIG. 7Ebeing the standard depth D_(ave) of 1.65 mm.

By setting the groove depth as shown in FIG. 7A, FIG. 7B, FIG. 7C, andFIG. 7D and FIG. 7E, FIG. 7F, FIG. 7G, and FIG. 7H, the generation of4th order, 5th order, 6th order, and 8th order propagating waves beingthe unnecessary vibration waves are substantially suppressed withrespect to the 7th order propagating wave. For example, when only the4th order unnecessary vibration wave is focused on, the center depth ofthe groove region 1012 has local maximum regions (deep regions) in 8portions and local minimum regions (shallow regions) in 8 portions at anequal interval (angle of π/4) with respect to the circumference as alsorepresented by the second term (sin(4×2×ω+θ₄)) of the right side of theexpression (1). The position of an antinode of each standing wavegenerated by the two drive phase electrodes 10231 is also shifted at anangle of π/4. Therefore, one standing wave vibrates in a portion havinga low rigidity, and hence the resonant frequency is shifted to a lowfrequency side. The other standing wave vibrates in a portion having ahigh rigidity, and hence the resonant frequency is shifted to a highfrequency side. The resonant frequencies of the standing waves areseparated, with the result that the 4th order propagating wave(unnecessary vibration wave) is not generated. The same mechanism ofsuppression applies to the other order unnecessary vibration waves.

As a method of confirming that the center depth of the groove regions1012 in the X portions in the vibrating plate 101 of the ultrasonicmotor changes along the curve obtained by superimposing one or more sinewaves on one another, there may be given the following method. First,coordinates and a depth of a center portion of each groove with respectto the circumferential length of the vibrating plate 101 on the outerdiameter side are actually measured. The coordinates of the grooveregions are taken on the horizontal axis, and the actually measureddepth is taken on the vertical axis. Plots are complemented, and a curvein which a groove depth is present in all the coordinates is assumed.This curve is subjected to Fourier transformation to determine thepresence and number of sine waves.

The center depth of the groove regions 1012 in the X portions changes sothat the number of the groove regions which reach a local maximum andthe number of the groove regions which reach a local minimum reaches 12or more, respectively. The local maximum of the center depth indicatesthat the center depth of a certain groove region is larger than anycenter depth of the groove regions adjacent to the certain groove regionon both sides. Similarly, the local minimum of the center depthindicates that the center depth of a certain groove region is smallerthan any center depth of the groove regions adjacent to the certaingroove region on both sides.

The ultrasonic motor and the vibrator 1 of the present invention use a7th order bending vibration wave as a drive source of the moving member2. The unnecessary vibration waves having significant adverse effectsare 6th order and 8th order vibration waves having resonant frequenciesclose to that of the 7th order bending vibration wave. As represented bythe fourth term of the right side of the expression (1), the 6th orderunnecessary vibration wave having particularly large effects can beeffectively suppressed by arranging 12 local maximum regions (deepregions) and 12 local minimum regions (shallow regions) in the grooveregions 1012.

It is preferred that the number of the groove regions 1012 which reach alocal maximum be matched with that of the groove regions 1012 whichreach a local minimum. It is preferred that the number of the grooveregions 1012 which reach a local maximum and the number of the grooveregions 1012 which reach a local minimum be 16 or less, respectively.When an attempt is made to suppress the 8th unnecessary vibration wave,the number of the groove regions 1012 which reach a local maximum andthe number of the groove regions 1012 which reach a local minimum maybecome 16, respectively. However, when the number becomes 17 or more,there is a risk in that the drive force generated by the ultrasonicmotor and the vibrator 1 of the present invention may extremelydecrease. It is more preferred that the number of the groove regions1012 which reach a local maximum be from 12 to 16. With suchconfiguration, the unnecessary vibration waves can be furthereffectively suppressed.

(Positional Relationship Between Local Maximum Region and Local MinimumRegion of Center Depth)

In the groove regions 1012 in the X portions, the groove region in whichthe center depth reaches a local maximum and the groove region in whichthe center depth reaches a local minimum are arranged so as to sandwichone or more groove regions without being adjacent to each other. Withthis configuration, the rotation operation of the moving member 2 at atime when the ultrasonic motor and the vibrator 1 of the presentinvention are driven becomes more stable.

When the ultrasonic motor and the vibrator 1 of the present inventionare driven, an elliptical motion occurs in a ceiling surface of eachprotrusion region 1011 to serve as power for rotating the moving member2. The elliptical ratio of the elliptical motion depends on the centerdepth of the groove region. Therefore, when the center depth is small,the elliptical ratio becomes larger, and when the center depth is large,the elliptical ratio becomes smaller. The elliptical ratio differsgreatly between the groove region in which the center depth reaches alocal maximum and the groove region in which the center depth reaches alocal minimum. Therefore, when those groove regions are adjacent to eachother, the rotation operation of the moving member 2 does not becomesmoother, and the behavior of the rotation operation varies depending onthe rotation direction.

It is preferred that, of the groove regions 1012 in the X portions whichreach a local maximum, a number I of the groove regions positionedbetween the groove region having a largest center depth and the grooveregion having a second largest center depth satisfy a relationship:I≧X/18. With such configuration, the elliptical ratio becomes moreuniform, and as a result, the rotation operation becomes even morestable, and the rotation speed increases.

It is preferred that, of the center depths D₁ to D_(X), a difference(change width) between the maximum value (groove having a largest centerdepth) and the minimum value (groove having a smallest center depth) be5% or more and 25% or less with respect to the maximum thickness T_(dia)of the vibrating plate 101. By setting the change width of the centerdepths D₁ to D_(X) to within the above-mentioned range with respect tothe maximum thickness T_(dia) of the vibrating plate 101, thesuppression of the unnecessary vibration waves and the efficiency of themotor drive can be achieved. When the difference between the maximumvalue and the minimum value of the center depths D₁ to D_(X) is smallerthan 5% with respect to the maximum thickness T_(dia), there is a riskin that the unnecessary vibration waves may not be sufficientlysuppressed. Meanwhile, when the difference between the maximum value andthe minimum value of the center depths D₁ to D_(X) is more than 25% withrespect to the maximum thickness T_(dia), the transmission efficiency ofvibration to the moving member 2 for each protrusion region 1011 varies,and hence there is a risk in that the drive efficiency of the motor maydecrease.

FIG. 7A, FIG. 7B, FIG. 7C, and FIG. 7D and FIG. 7E, FIG. 7F, FIG. 7G,and FIG. 7H are each an example in which the center depth is designed sothat the difference between the maximum value and the minimum value ofthe center depths D₁ to D_(X) is 5% or more and 25% or less with respectto the maximum thickness T_(dia), with the maximum thickness T_(dia)being set to 4 mm or more and 6 mm or less.

It is preferred that the standard depth D_(ave) of the center depths D₁to D_(X) be 25% or more and 50% or less with respect to the maximumthickness T_(dia). By setting the standard depth D_(ave) to within theabove-mentioned range with respect to the maximum thickness T_(dia) ofthe vibrating plate 101, the efficiency of the motor drive and therotation speed can be achieved. When the standard depth D_(ave) issmaller than 25% with respect to the maximum thickness T_(dia), thedeformation amount during drive of the vibrating plate 101 decreases,and there is a risk in that the rotation speed of the motor maydecrease. Meanwhile, when the standard depth D_(ave) is more than 50%with respect to the maximum thickness T_(dia), there is a risk in thatthe drive efficiency of the motor may decrease.

It is preferred that, of the groove regions in which the center depthreaches a local maximum, 8 or more groove regions have the center depthof 1.15 times or more and 1.30 times or less of the standard depthD_(ave). With such configuration, a load is uniformly applied to eachgroove, and hence the rotation speed increases particularly in a highload.

When the number X is an even number, it is preferred that, of the centerdepths D₁ to D_(X), the depth change of the former half D₁ to D_(X/2)(rows of center depths of the respective groove regions) be matched withthat of the latter half D_(X/2+1) to D_(X). The groove region 1012serving as a starting point may be arbitrarily selected. Therefore, whenX is equal to, for example, 90, it is preferred that a relationship:D_(n)=D_(n+45) hold with respect to any n. In this case, the depthchange of 45 continuous groove regions 1012 and the depth change of 45remaining continuous groove regions 1012 are matched in the samecircumferential direction. With such configuration, the suppression ofthe unnecessary vibration waves is further enhanced, and the symmetricproperty of the rotation motion of the moving member 2 becomessatisfactory.

Of the groove regions 1012 in the X portions, the center depth of thegroove region 1012 closest to the detection phase electrode 10233 isrepresented by D_(sen)(unit: mm). The term “sen” as used herein relatesto a natural number of 1 or more and X or less. The groove region 1012closest to the detection phase electrode 10233 is determined with thecenter of the detection phase electrode 10233 being a reference point.The center depths of two groove regions 1012 adjacent to the grooveregion 1012 closest to the detection phase electrode 10233 arerepresented by D_(sen−1) and D_(sen+1). In this case, it is preferredthat |D_(sen+1)−D_(sen−1)|/D_(sen) be 5% or less. When the relationshipof the center depths of the three groove regions is set to within theabove-mentioned range, the center depths of both the adjacent grooveregions 1012 having the detection phase electrode 10233 as a centerbecome closer to each other. As a result, the amplitude of the vibrator1 in the vicinity of the detection phase electrode 10233 during drive ofthe ultrasonic motor becomes substantially the same irrespective ofwhether the drive is clockwise drive or counterclockwise drive, andhence the drive control of the ultrasonic motor by the drive circuitbecomes easier.

The ultrasonic motor using a 7th order bending vibration wave isdescribed above as an example, but the present invention is alsoapplicable to a case using another order bending vibration wave. Forexample, unnecessary vibration waves other than the 6th orderunnecessary vibration wave may be suppressed in an ultrasonic motorusing a 6th order bending vibration wave. Similarly, the presentinvention can be applied to ultrasonic motors using any bendingvibration waves such as a 8th order bending vibration wave and a 11thorder bending vibration wave.

(Drive Control System)

Next, the drive control system of the present invention is described.FIG. 8 is a schematic view for illustrating the drive control systemaccording to an embodiment of the present invention.

The drive control system of the present invention has a feature ofincluding at least the ultrasonic motor of the present invention and adrive circuit electrically connected to the ultrasonic motor. The drivecircuit includes a signal generation unit configured to generate anelectric signal for generating a 7th order bending vibration wave in theultrasonic motor of the present invention to cause rotation drive.

The drive circuit simultaneously applies alternating voltages having thesame frequency and a temporal phase difference of π/2 to each drivephase electrode 10231 (phase A and phase B) of the ultrasonic motor. Asa result, standing waves generated in the phase A and the phase B aresynthesized to generate a propagating wave of a 7th order bendingvibration wave (wavelength: λ), which propagates in the circumferentialdirection, on the second surface of the vibrating plate 101.

In this case, each point on the protrusion regions 1011 in the Xportions of the vibrating plate 101 undergoes elliptical motion.Therefore, the moving member 2 rotates due to the friction force in thecircumferential direction from the vibrating plate 101. When the 7thorder bending propagating wave is generated, the detection phaseelectrode 10233 generates a detection signal in accordance with theamplitude of vibration of the piezoelectric ceramic piece 1021 in theregions brought into contact with the detection phase electrode 10233and outputs the detection signal to the drive circuit through wiring.The drive circuit compares the detection signal with the phase of thedrive signal input to the drive phase electrode 10231, to thereby graspa shift from a resonant state. By determining again the frequency of thedrive signal input to the drive phase electrode 10231 based on theabove-mentioned information, the feedback control of the ultrasonicmotor can be performed.

(Optical Apparatus)

Next, the optical apparatus of the present invention is described. Theoptical apparatus of the present invention includes at least the drivecontrol system of the present invention and an optical elementdynamically connected to the ultrasonic motor included in the drivecontrol system.

The phrase “dynamic connection” as used herein refers to a state inwhich elements are directly in contact with each other or a state inwhich the elements are in contact with each other through intermediationof a third element so that force generated by a coordinate change, avolume change, and a shape change of one element is transmitted to theother element.

FIG. 9A and FIG. 9B are each a sectional view of main parts of aninterchangeable lens barrel for a single-lens reflex camera as anexample of an optical apparatus according to an exemplary embodiment ofthe present invention. FIG. 10 is an exploded perspective view of theinterchangeable lens barrel for the single-lens reflex camera as theexample of the optical apparatus according to the exemplary embodimentof the present invention. A fixed barrel 712, a linear guide barrel 713,and a front lens unit barrel 714 holding a front lens group 701 arefixed to a detachable mount 711 for a camera. Those components are fixedelements of the interchangeable lens barrel.

A linear guide groove 713 a in an optical axis direction for a focuslens 702 is formed on the linear guide barrel 713. Cam rollers 717 a and717 b protruding outward in a radial direction are fixed to a rear lensunit barrel 716 holding the focus lens 702 via axial screws 718, and thecam roller 717 a is fitted in the linear guide groove 713 a.

A cam ring 715 is fitted on the inner periphery of the linear guidebarrel 713 in a rotatable manner. Relative movement between the linearguide barrel 713 and the cam ring 715 in the optical axis direction isrestricted due to a roller 719 fixed to the cam ring 715 being fitted inan annular groove 713 b of the linear guide barrel 713. A cam groove 715a for the focus lens 702 is formed on the cam ring 715, and theabove-mentioned cam roller 717 b is simultaneously fitted in the camgroove 715 a.

On the outer peripheral side of the fixed barrel 712, there is arrangeda rotation transmission ring 720 held by a ball race 727 in a rotatablemanner at a predetermined position with respect to the fixed barrel 712.The rotation transmission ring 720 has shafts 720 f extending radiallyfrom the rotation transmission ring 720, and rollers 722 are held by theshafts 720 f in a rotatable manner. A large diameter region 722 a of theroller 722 makes contact with a mount side end surface 724 b of a manualfocus ring 724. In addition, a small diameter part 722 b of the roller722 makes contact with a joining member 729. Six rollers 722 arearranged on the outer periphery of the rotation transmission ring 720 atuniform intervals, and each roller is provided in the relationship asdescribed above.

A low friction sheet (washer member) 733 is arranged on an innerdiameter region of the manual focus ring 724, and this low frictionsheet is sandwiched between a mount side end surface 712 a of the fixedbarrel 712 and a front side end surface 724 a of the manual focus ring724. In addition, an outer diameter surface of the low friction sheet733 is formed into a ring shape so as to be circumferentially fitted onan inner diameter region 724 c of the manual focus ring 724. Further,the inner diameter region 724 c of the manual focus ring 724 iscircumferentially fitted on an outer diameter region 712 b of the fixedbarrel 712. The low friction sheet 733 has a role of reducing frictionin a rotation ring mechanism in which the manual focus ring 724 rotatesrelatively to the fixed barrel 712 about the optical axis.

Note that, the large diameter region 722 a of the roller 722 makescontact with the mount side end surface 724 b of the manual focus ringunder a state in which a pressure is applied by a pressing force of awave washer 726 pressing an ultrasonic motor 725 to the front of thelens. In addition, similarly, the small diameter region 722 b of theroller 722 makes contact with the joining member 729 under a state inwhich an appropriate pressure is applied by a pressing force of the wavewasher 726 pressing the ultrasonic motor 725 to the front of the lens.Movement of the wave washer 726 in the mount direction is restricted bya washer 732 connected to the fixed barrel 712 by bayonet joint. Aspring force (biasing force) generated by the wave washer 726 istransmitted to the ultrasonic motor 725, and further to the roller 722,to be a force for the manual focus ring 724 to press the mount side endsurface 712 a of the fixed barrel 712. In other words, the manual focusring 724 is integrated under a state in which the manual focus ring 724is pressed to the mount side end surface 712 a of the fixed barrel 712via the low friction sheet 733.

Therefore, when a drive circuit having a signal generation unit builttherein (not shown) drives the ultrasonic motor 725 to rotate withrespect to the fixed barrel 712, the rollers 722 rotate about the shafts720 f so that the joining member 729 is brought into contact by frictionwith the small diameter regions 722 b of the rollers 722. As a result ofthe rotation of the rollers 722 about the shafts 720 f, the rotationtransmission ring 720 rotates about the optical axis (automatic focusoperation).

In addition, when a manual operation input unit (not shown) gives arotation force about the optical axis to the manual focus ring 724, thecomponents are operated as follows.

Specifically, the rollers 722 rotate about the shafts 720 f by frictionforce because the mount side end surface 724 b of the manual focus ring724 is brought into pressure-contact with the large diameter regions 722a of the rollers 722. When the large diameter regions 722 a of therollers 722 rotate about the shafts 720 f, the rotation transmissionring 720 rotates about the optical axis. In this case, the ultrasonicmotor 725 does not rotate because of a friction retaining force betweena moving member 725 c and a vibrator 725 b (manual focus operation).

Two focus keys 728 are mounted to the rotation transmission ring 720 atopposing positions, and the focus key 728 is fitted to a notch portion715 b formed in the tip of the cam ring 715. Therefore, when theautomatic focus operation or the manual focus operation is performed sothat the rotation transmission ring 720 is rotated about the opticalaxis, the rotation force is transmitted to the cam ring 715 via thefocus key 728. When the cam ring 715 is rotated about the optical axis,the rear lens unit barrel 716 whose rotation is restricted by the camroller 717 a and the linear guide groove 713 a is moved forward andbackward along the cam groove 715 a of the cam ring 715 by the camroller 717 b. Thus, the focus lens 702 is driven, and the focusoperation is performed. That is, the position of the focus lens 702,which is an optical element, is changed by the focus lens 702 beingdynamically connected to the ultrasonic motor 725.

In this case, the interchangeable lens barrel for the single-lens reflexcamera is described above as the optical apparatus of the presentinvention, but the present invention can be applied to many kinds ofoptical apparatus including the ultrasonic motor, regardless of a typeof the camera, including a compact camera, an electronic still camera,and the like.

EXAMPLES

Next, the vibrator, the ultrasonic motor, the drive control system, andthe optical apparatus of the present invention are specificallydescribed by means of Examples, but the present invention is not limitedto the following Examples. The Examples are described with reference tothe drawings with use of the reference symbols in the drawings.

(Manufacturing Example of Annular Piezoelectric Ceramic Piece)

An annular piezoelectric ceramic piece containing lead in a content ofless than 1,000 ppm and having a Young's modulus at room temperature of80 GPa or more and 125 GPa or less was manufactured in the followingmanner. The Young's modulus was measured through use of a test piece cutout from a piezoelectric element.

(Manufacturing Example of KNN-Based Piezoelectric Ceramics)

With intent to add Cu to[{Ba_(0.75)(Bi_(0.5)Na_(0.5))_(0.25)}_(0.08)(Na_(0.49)Li_(0.02)K_(0.49))_(0.92)]_(1.00){(Ti_(0.20)Zr_(0.75)Hf_(0.05))_(0.08)(Nb_(0.90)Ta_(0.10))_(0.92)}O₃corresponding to the composition of h of 0.08, j of 0.49, k of 0.02, uof 0.75, v of 0.05, w of 0.10, and m of 0 in the general formula (1),with the metal M being Ba_(0.75) (Bi_(0.5)Na_(0.5))_(0.25),corresponding raw material powders were weighed as follows.

Barium carbonate, bismuth oxide, sodium carbonate, lithium carbonate,potassium carbonate, titanium oxide, zirconium oxide, hafnium oxide,niobium pentoxide, and tantalum pentoxide, each being commerciallyavailable with a purity of 99.9% or more, serving as raw materialpowders, were weighed so that Ba, Bi, Na, Li, K, Ti, Zr, Hf, Nb, and Tasatisfied the composition of[{Ba_(0.75)(Bi_(0.5)Na_(0.5))_(0.25)}_(0.08)(Na_(0.49)Li_(0.02)K_(0.49))_(0.92)]_(1.00){(Ti_(0.20)Zr_(0.75)Hf_(0.05))_(0.08)(Nb_(0.90)Ta_(0.10))_(0.92)}O₃.The composition was able to be sintered at low temperature, and hencethe loading ratio was set as intended without considering thevolatilization of alkali metal components during the sintering step.Manganese dioxide was weighed so that the content of Mn was 0.25 part byweight with respect to 100 parts by weight of the composition of[{Ba_(0.75)(Bi_(0.5)Na_(0.5))_(0.25)}_(0.08)(Na_(0.49)Li_(0.02)K_(0.49))_(0.92)]_(1.00){(Ti_(0.20)Zr_(0.75)Hf_(0.05))_(0.08)(Nb_(0.90)Ta_(0.10))_(0.92)}O₃.

Those weighed powders were mixed by dry blending for 24 hours throughuse of a ball mill to provide mixed powder. In order to granulate theobtained mixed powder, 3 parts by weight of a PVA binder with respect tothe mixed powder was caused to adhere to the surface of the mixed powderthrough use of a spray dryer, to thereby provide granulated powder.

Next, the obtained granulated powder was supplied to a mold, and amolding pressure of 200 MPa was applied to the granulated powder throughuse of a press molding machine to produce a disc-shaped molding. Thedimensions of the mold used for the disc-shaped molding had a margin of2 mm, 2 mm, and 0.5 mm with respect to the outer diameter, the innerdiameter, and the thickness of the intended disc-shaped piezoelectricceramics, respectively.

The obtained molding was placed in an electric furnace and held at ahighest temperature of 1,000° C. for 10 hours, to thereby sinter themolding in an atmospheric atmosphere over a total of 48 hours. Next, thesintered body was ground into an annular shape having a desired outerdiameter, inner diameter, and thickness to provide an annularpiezoelectric ceramic piece.

Piezoelectric ceramic pieces, which were manufactured so as to have anouter diameter within a range of from 54 mm to 90 mm, an inner diameterwithin a range of from 38 mm to 84 mm, and a thickness within a range offrom 0.3 mm to 1.0 mm, were able to have equivalent piezoelectriccharacteristics. The vibrator and the ultrasonic motor of the presentinvention can be manufactured through use of a piezoelectric ceramicpiece having any dimensions within the above-mentioned ranges. However,for convenience of description, an annular piezoelectric ceramic piecehaving an outer diameter of 77.0 mm, an inner diameter of 67.1 mm, and athickness of 0.5 mm is described as a typical example.

The average circle equivalent diameter and the relative density ofcrystal grains forming the manufactured piezoelectric ceramic piece wereevaluated, and a piezoelectric ceramic piece having an average circleequivalent diameter of from 0.5 μm to 10.0 μm and a relative density of95% or more was used for manufacturing a piezoelectric element in thenext step. For calculation of the average circle equivalent diameter, apolarization microscope and a scanning electron microscope were used.The relative density was measured by the Archimedes' method andevaluated with respect to a theoretical density calculated from alattice constant of the piezoelectric ceramic piece and an atomic weightof a constituent element of the piezoelectric ceramic piece.

It was found from the X-ray diffraction measurement of an annularsurface that any of the piezoelectric ceramic pieces manufactured by theabove-mentioned method had a perovskite structure.

The composition of the piezoelectric ceramic piece was evaluated by ICPemission spectroscopic analysis. As a result, the content of lead of anyof the piezoelectric ceramic pieces manufactured by the above-mentionedmethod was less than 5 ppm. Through the combination of the results ofICP emission spectroscopic analysis and X-ray diffraction measurement,it was found that the composition of the piezoelectric ceramic piececontained, as a main component, a perovskite type metal oxide which canbe represented by the composition of[{Ba_(0.75)(Bi_(0.5)Na_(0.5))_(0.25)}_(0.08)(Na_(0.49)Li_(0.02)K_(0.49))_(0.92)]_(1.00){(Ti_(0.20)Zr_(0.75)Hf_(0.05))_(0.08)(Nb_(0.90)Ta_(0.10))_(0.92)}O₃and contained 0.25 part by weight of Mn with respect to 100 parts byweight of the main component.

(Manufacturing Example of BCTZ-Based Piezoelectric Ceramics)

With intent to add Mn and Bi to(Ba_(0.84)Ca_(0.16))_(1.006)(Ti_(0.94)Zr_(0.06))O₃ corresponding to thecomposition of s of 0.16, t of 0.06, and a of 1.006 in the generalformula (2), corresponding raw material powders were weighed as follows.

Barium titanate, calcium titanate, and calcium zirconate each having anaverage particle diameter of 300 nm or less and a perovskite typestructure, serving as raw material powders, were weighed so that Ba, Ca,Ti, and Zr satisfied the composition of(Ba_(0.84)Ca_(0.16))_(1.006)(Ti_(0.94)Zr_(0.06))O₃. In order to adjust“α” representing the molar ratio of the A-site and the B-site, bariumcarbonate and titanium oxide were used. Trimanganese tetroxide wasweighed so that the content of Mn was 0.18 part by weight in terms of ametal with respect to 100 parts by weight of the composition of(Ba_(0.84)Ca_(0.16))_(1.006)(Ti_(0.94)Zr_(0.06))O₃. Similarly, bismuthoxide was weighed so that the content of Bi was 0.26 part by weight interms of a metal.

Those weighed powders were mixed by dry blending for 24 hours throughuse of a ball mill to provide mixed powder. In order to granulate theobtained mixed powder, 3 parts by weight of a PVA binder with respect tothe mixed powder was caused to adhere to the surface of the mixed powderthrough use of a spray dryer, to thereby provide granulated powder.

Next, the obtained granulated powder was supplied to a mold, and amolding pressure of 200 MPa was applied to the granulated powder throughuse of a press molding machine to produce a disc-shaped molding. Thedimensions of the mold used for the disc-shaped molding had a margin of2 mm, 2 mm, and 0.5 mm with respect to the outer diameter, the innerdiameter, and the thickness of intended disc-shaped piezoelectricceramics, respectively.

The obtained molding was placed in an electric furnace and held at ahighest temperature of 1,380° C. for 5 hours, to thereby sinter themolding in an atmospheric atmosphere over a total of 24 hours. Next, thesintered body was ground into an annular shape having a desired outerdiameter, inner diameter, and thickness to provide an annularpiezoelectric ceramic piece.

Piezoelectric ceramic pieces, which were manufactured so as to have anouter diameter within a range of from 54 mm to 90 mm, an inner diameterwithin a range of from 38 mm to 84 mm, and a thickness within a range offrom 0.3 mm to 1.0 mm, were able to have equivalent piezoelectriccharacteristics. The vibrator and the ultrasonic motor of the presentinvention can be manufactured through use of a piezoelectric ceramicpiece having any dimensions within the above-mentioned ranges. However,for convenience of description, an annular piezoelectric ceramic piecehaving an outer diameter of 77.0 mm, an inner diameter of 67.1 mm, and athickness of 0.5 mm is described as a typical example.

The average circle equivalent diameter and the relative density ofcrystal grains forming the manufactured piezoelectric ceramic piece wereevaluated, and a piezoelectric ceramic piece having an average circleequivalent diameter of from 0.7 μm to 3.0 μm and a relative density of95% or more was used for manufacturing a piezoelectric element in thenext step. For calculation of the average circle equivalent diameter, apolarization microscope and a scanning electron microscope were used.The relative density was measured by the Archimedes' method andevaluated with respect to a theoretical density calculated from alattice constant of the piezoelectric ceramic piece and an atomic weightof a constituent element of the piezoelectric ceramic piece.

It was found from the X-ray diffraction measurement of an annularsurface that any of the piezoelectric ceramic pieces manufactured by theabove-mentioned method had a tetragonal perovskite structure.

The composition of the piezoelectric ceramic piece was evaluated by ICPemission spectroscopic analysis. As a result, the content of lead of anyof the piezoelectric ceramic pieces manufactured by the above-mentionedmethod was less than 1 ppm. Through the combination of the results ofICP emission spectroscopic analysis and X-ray diffraction measurement,it was found that the composition of the piezoelectric ceramic piececontained, as a main component, a perovskite type metal oxide which canbe represented by the composition of(Ba_(0.84)Ca_(0.16))_(1.006)(Ti_(0.94)Zr_(0.06))O₃ and contained 0.18part by weight of Mn and 0.26 part by weight of Bi with respect to 100parts by weight of the main component.

(Manufacturing Example 1 of Vibrating Plate)

FIG. 11A and FIG. 11B are each a schematic step view for illustrating anexample of a method of manufacturing an annular vibrating plate to beused in the ultrasonic motor and the vibrator of the present invention.

In order to manufacture a vibrating plate to be used in the presentinvention, an annular metal plate 101 a as illustrated in FIG. 11A wasprepared. The metal plate 101 a is formed of magnetic stainless steelSUS420J2 of JIS. SUS420J2 is martensite stainless steel that is an alloycontaining 70 mass % or more of steel and 12 mass % to 14 mass % ofchromium.

The outer diameter, inner diameter, and maximum thickness of the metalplate 101 a were set to intended values of the outer diameter 2R, theinner diameter 2R_(in), and the maximum thickness T_(dia) of thevibrating plate 101 illustrated in FIG. 11B. A vibrating plateapplicable to the vibrator and the ultrasonic motor of the presentinvention was able to be manufactured with the metal plate 101 a havingan outer diameter (2R) within a range of from 56 mm to 90 mm, an innerdiameter within a range of from 40 mm to 84 mm, and a thickness within arange of from 4 mm to 6 mm. In this manufacturing example, forconvenience of description, the metal plate 101 a having the outerdiameter 2R of 77 mm, the inner diameter 2R_(in) of 67.1 mm, and themaximum thickness T_(dia) of 5.0 mm is described as a typical example.

Next, 90 (X=90) groove regions 1012 were mechanically formed in a radialmanner by grinding one surface (second surface) of the annular metalplate 101 a (grooving step). The metal plate 101 a after grooving wassubjected to barrel treatment, lapping, and electroless nickel plating,to thereby provide the vibrating plate 101 to be used in the vibrator 1of the present invention.

The groove region 1012 of the vibrating plate 101 was formed into arectangular parallelepiped shape having a width of 0.895 mm when viewedfrom the second surface side. Therefore, the protrusion region 1011 wasformed into a fan shape having a width enlarged on the annular outerdiameter side. As a result, the average value L_(top) of the length ofthe protrusion region 1011 in the circumferential direction on the outerdiameter side and the average value L_(btm) of the length of the grooveregion 1012 in the circumferential direction on the outer diameter sidehad a relationship: L_(top)/L_(btm)=2.00.

Center depths D₁ to D₉₀ of the 90 groove regions 1012 of the vibratingplate 101 were set to depths as shown in FIG. 7A. That is, the centerdepths D₁ to D₉₀ change so as to follow a curve obtained bysuperimposing four sine waves on one another. As is understood from FIG.7A and FIG. 7B corresponding to FIG. 7A, the numbers of local maximumregions and local minimum regions of the change were 12, respectively.The local maximum regions and the local minimum regions of the changewere not adjacent to each other. The maximum absolute value of thecenter depths D₁ to D₉₀ was 2.216 mm, and the minimum absolute valuethereof was 1.493 mm. Therefore, a difference therebetween was 0.722 mm,which was 14.45% with respect to the maximum thickness T_(dia) (5.0 mm)of the vibrating plate 101. The average of the absolute values of thecenter depths D₁ to D₉₀ was 1.85 mm, which was 37.0% with respect to themaximum thickness T_(dia) (5.0 mm) of the vibrating plate 101.

Of the groove regions 1012 in which the center depth reaches a localmaximum, the groove region 1012 having a largest center depth wasD₃₀=D₇₅=2.216 mm, and the groove region 1012 having a second largestcenter depth was D₈=D₆₃=2.164 mm. The number I of the groove regions1012 positioned between the groove region 1012 having a largest centerdepth and the groove region 1012 having a second largest center depthwas 11 at a minimum.

Of the groove regions in which the center depth reaches a local maximum,6 groove regions have the center depths D₁₈, D₃₀, D₄₀, D₆₃, D₇₅, and D₈₅of 1.15 times or more and 1.30 times or less of the standard depthD_(ave).

The depth change of the center depths D₁ to D₄₅ and the depth change ofthe center depths D₄₆ to D₉₀ were as shown in Table 1. In Table 1, asuffix of D_(X) is shown in a large size so that the suffix can beeasily recognized visually. As is understood from Table 1, of the centerdepths D₁ to D₉₀, the change in the center depths D₁ to D_(90/2) wasmatched with the change in the center depths D_(90/2+1) to D₉₀. Withsuch configuration, the unnecessary vibration waves other than the 7thorder vibration wave can be further suppressed.

TABLE 1 Symbol of center Symbol of center depth of groove Groove depthdepth of groove Groove depth region [mm] region [mm] D30 2.216 D75 2.216D18 2.164 D63 2.164 D40 2.160 D85 2.160 D19 2.117 D64 2.117 D1 2.115 D462.115 D29 2.108 D74 2.108 D31 2.099 D76 2.099 D2 2.083 D47 2.083 D392.046 D84 2.046 D41 2.045 D86 2.045 D8 2.028 D53 2.028 D9 2.027 D542.027 D10 2.006 D55 2.006 D11 1.991 D56 1.991 D17 1.975 D62 1.975 D71.927 D52 1.927 D20 1.924 D65 1.924 D12 1.918 D57 1.918 D23 1.906 D681.906 D45 1.898 D90 1.898 D32 1.891 D77 1.891 D24 1.881 D69 1.881 D381.834 D83 1.834 D3 1.832 D48 1.832 D28 1.823 D73 1.823 D22 1.818 D671.818 D21 1.792 D66 1.792 D42 1.772 D87 1.772 D33 1.747 D78 1.747 D131.741 D58 1.741 D6 1.723 D51 1.723 D25 1.708 D70 1.708 D34 1.702 D791.702 D37 1.691 D82 1.691 D35 1.689 D80 1.689 D16 1.676 D61 1.676 D361.666 D81 1.666 D44 1.635 D89 1.635 D4 1.591 D49 1.591 D43 1.575 D881.575 D27 1.574 D72 1.574 D5 1.556 D50 1.556 D14 1.543 D59 1.543 D261.543 D71 1.543 D15 1.493 D60 1.493

(Manufacturing Example 2 of Vibrating Plate)

A vibrating plate V2 was manufactured through use of the same rawmaterials and manufacturing method as those of the vibrating plate V1.The vibrating plate V2 was manufactured so as to satisfyL_(top)/L_(btm)=2.40.

The center depths D₁ to D₉₀ of the 90 groove regions 1012 of thevibrating plate 101 were set to those shown in FIG. 7D. That is, thecenter depths D₁ to D₉₀ change so as to follow a curve obtained bysuperimposing four sine waves on one another. As is understood from FIG.7D and FIG. 7C corresponding to FIG. 7D, the numbers of local maximumregions and local minimum regions of the change were 12, respectively.The local maximum regions and the local minimum regions of the changewere not adjacent to each other. The maximum absolute value of thecenter depths D₁ to D₉₀ was 2.202 mm, and the minimum absolute valuethereof was 1.498 mm. Therefore, a difference therebetween was 0.703 mm,which was 14.1% with respect to the maximum thickness T_(dia) (5.0 mm)of the vibrating plate 101. The average of the absolute values of thecenter depths D₁ to D₉₀ was 1.85 mm, which was 37.0% with respect to themaximum thickness T_(dia) (5.0 mm) of the vibrating plate 101.

Of the groove regions 1012 in which the center depth reaches a localmaximum, the groove region 1012 having a largest center depth wasD₃₀=D₇₅=2.202 mm, and the groove region 1012 having a second largestcenter depth was D₈=D₆₃=2.169 mm. The number I of the groove regions1012 positioned between the groove region 1012 having a largest centerdepth and the groove region 1012 having a second largest center depthwas 9 at minimum.

Of the groove regions 1012 in which the center depth reaches a localmaximum, there were 8 groove regions 1012 in which the center depth is1.15 times or more and 1.30 times or less of the standard depth D_(ave)in the regions of the depths D₁, D₁₈, D₃₀, D₄₀, D₄₆, D₆₃, D₇₅, and D₈₅.

The change in the center depths D₁ to D₄₅ and the change in the centerdepths D₄₆ to D₉₀ were as shown in Table 2. In Table 2, a suffix ofD_(X) is shown in a large size so that the suffix can be easilyrecognized visually. As is understood from Table 2, of the center depthsD₁ to D₉₀, the change in the center depths D₁ to D_(90/2) was matchedwith the change in the center depths D_(90/2+1) to D₉₀. With suchconfiguration, the unnecessary vibration waves other than the 7th ordervibration wave can be further suppressed.

TABLE 2 Symbol of center Symbol of center depth of groove Groove depthdepth of groove Groove depth region [mm] region [mm] D30 2.202 D75 2.202D40 2.169 D85 2.169 D18 2.140 D63 2.140 D29 2.135 D74 2.135 D1 2.131 D462.131 D39 2.094 D84 2.094 D31 2.070 D76 2.070 D19 2.053 D64 2.053 D22.037 D47 2.037 D11 2.017 D56 2.017 D10 2.014 D55 2.014 D17 2.006 D622.006 D9 2.002 D54 2.002 D41 1.999 D86 1.999 D8 1.998 D53 1.998 D451.962 D90 1.962 D23 1.955 D68 1.955 D7 1.933 D52 1.933 D12 1.923 D571.923 D22 1.888 D67 1.888 D32 1.885 D77 1.885 D20 1.883 D65 1.883 D281.868 D73 1.868 D38 1.867 D83 1.867 D24 1.865 D69 1.865 D21 1.816 D661.816 D3 1.774 D48 1.774 D33 1.770 D78 1.770 D6 1.766 D51 1.766 D161.722 D61 1.722 D34 1.721 D79 1.721 D13 1.715 D58 1.715 D42 1.713 D871.713 D44 1.686 D89 1.686 D37 1.679 D82 1.679 D35 1.674 D80 1.674 D251.647 D70 1.647 D36 1.631 D81 1.631 D5 1.593 D50 1.593 D27 1.585 D721.585 D4 1.577 D49 1.577 D43 1.564 D88 1.564 D14 1.518 D59 1.518 D151.506 D60 1.506 D26 1.498 D71 1.498

(Manufacturing Example 3 of Vibrating Plate)

A vibrating plate V3 was manufactured through use of the same rawmaterials and manufacturing method as those of the vibrating plate V1.The vibrating plate V3 was manufactured so as to satisfy T_(dia)=6.0 mm,D_(ave)=1.65 mm and L_(top)/L_(btm)=2.40.

The center depths D₁ to D₉₀ of the 90 groove regions 1012 of thevibrating plate 101 were set to those shown in FIG. 7F. That is, thecenter depths D₁ to D₉₀ change so as to follow a curve obtained bysuperimposing four sine waves on one another. As is understood from FIG.7F and FIG. 7E corresponding to FIG. 7F, the numbers of local maximumregions and local minimum regions of the change were 12, respectively.The local maximum regions and the local minimum regions of the changewere not adjacent to each other. The maximum absolute value of thecenter depths D₁ to D₉₀ was 2.016 mm, and the minimum absolute valuethereof was 1.292 mm. Therefore, a difference therebetween was 0.724 mm,which was 12.1% with respect to the maximum thickness T_(dia) (6.0 mm)of the vibrating plate 101. The average of the absolute values of thecenter depths D₁ to D₉₀ was 1.65 mm, which was 27.5% with respect to themaximum thickness T_(dia) (6.0 mm) of the vibrating plate 101.

Of the groove regions 1012 in which the center depth reaches a localmaximum, the groove region 1012 having a largest center depth wasD₃₀=D₇₅=2.016 mm, and the groove region 1012 having a second largestcenter depth was D₈=D₆₃=1.963 mm. The number I of the groove regions1012 positioned between the groove region 1012 having a largest centerdepth and the groove region 1012 having a second largest center depthwas 11 at minimum.

Of the groove regions 1012 in which the center depth reaches a localmaximum, there were 8 groove regions 1012 in which the center depth is1.15 times or more and 1.30 times or less of the standard depth D_(ave)in the regions of the depths D₁, D₁₈, D₃₀, D₄₀, D₄₆, D₆₃, D₇₅, and D₈₅.

The change in the center depths D₁ to D₄₅ and the change in the centerdepths D₄₆ to D₉₀ were as shown in Table 3. In Table 3, a suffix ofD_(X) is shown in a large size so that the suffix can be easilyrecognized visually. As is understood from Table 3, of the center depthsD₁ to D₉₀, the change in the center depths D₁ to D_(90/2) was matchedwith the change in the center depths D_(90/2+1) to D₉₀. With suchconfiguration, the unnecessary vibration waves other than the 7th ordervibration wave can be further suppressed.

TABLE 3 Symbol of center Symbol of center depth of groove Groove depthdepth of groove Groove depth region [mm] region [mm] D30 2.016 D75 2.016D18 1.963 D63 1.963 D40 1.960 D85 1.960 D19 1.920 D64 1.920 D1 1.913 D461.913 D29 1.903 D74 1.903 D31 1.903 D76 1.903 D2 1.886 D47 1.886 D411.850 D86 1.850 D39 1.843 D84 1.843 D8 1.828 D53 1.828 D9 1.828 D541.828 D10 1.806 D55 1.806 D11 1.791 D56 1.791 D17 1.770 D62 1.770 D201.728 D65 1.728 D7 1.724 D52 1.724 D12 1.720 D57 1.720 D23 1.705 D681.705 D32 1.695 D77 1.695 D45 1.693 D90 1.693 D24 1.683 D69 1.683 D31.638 D48 1.638 D38 1.630 D83 1.630 D28 1.617 D73 1.617 D22 1.617 D671.617 D21 1.593 D66 1.593 D42 1.578 D87 1.578 D33 1.548 D78 1.548 D131.545 D58 1.545 D6 1.519 D51 1.519 D25 1.512 D70 1.512 D34 1.502 D791.502 D37 1.489 D82 1.489 D35 1.489 D80 1.489 D16 1.471 D61 1.471 D361.466 D81 1.466 D44 1.432 D89 1.432 D4 1.394 D49 1.394 D43 1.377 D881.377 D27 1.371 D72 1.371 D5 1.354 D50 1.354 D14 1.346 D59 1.346 D261.344 D71 1.344 D15 1.292 D60 1.292

(Manufacturing Example 4 of Vibrating Plate)

A vibrating plate V4 was manufactured through use of the same rawmaterials and manufacturing method as those of the vibrating plate V1.The vibrating plate V4 was manufactured so as to satisfyL_(top)/L_(btm)=2.86.

The center depths D₁ to D₉₀ of the 90 groove regions 1012 of thevibrating plate 101 were set to those shown in FIG. 7H. That is, thecenter depths D₁ to D₉₀ change so as to follow a curve obtained bysuperimposing four sine waves on one another. As is understood from FIG.7H and FIG. 7G corresponding to FIG. 7H, the numbers of local maximumregions and local minimum regions of the change were 12, respectively.The local maximum regions and the local minimum regions of the changewere not adjacent to each other. The maximum absolute value of thecenter depths D₁ to D₉₀ was 2.180 mm, and the minimum absolute valuethereof was 1.494 mm. Therefore, a difference therebetween was 0.687 mm,which was 13.7% with respect to the maximum thickness T_(dia) (5.0 mm)of the vibrating plate 101. The average of the absolute values of thecenter depths D₁ to D₉₀ was 1.85 mm, which was 37.0% with respect to themaximum thickness T_(dia) (5.0 mm) of the vibrating plate 101.

Of the groove regions 1012 in which the center depth reaches a localmaximum, the groove region 1012 having a largest center depth wasD₃₀=D₇₅=2.180 mm, and the groove region 1012 having a second largestcenter depth was D₄₀=D₈₅=2.177 mm. The number I of the groove regions1012 positioned between the groove region 1012 having a largest centerdepth and the groove region 1012 having a second largest center depthwas 9 at minimum.

Of the groove regions 1012 in which the center depth reaches a localmaximum, there were 6 groove regions 1012 in which the center depth is1.15 times or more and 1.30 times or less of the standard depth D_(ave)in the regions of the depths D₁₈, D₃₀, D₄₀, D₆₃, D₇₅, and D₈₅.

The change in the center depths D₁ to D₄₅ and the change in the centerdepths D₄₆ to D₉₀ were as shown in Table 4. In Table 4, a suffix ofD_(X) is shown in a large size so that the suffix can be easilyrecognized visually. As is understood from Table 4, of the center depthsD₁ to D₉₀, the change in the center depths D₁ to D_(90/2) was matchedwith the change in the center depths D_(90/2+1) to D₉₀. With suchconfiguration, the unnecessary vibration waves other than the 7th ordervibration wave can be further suppressed.

TABLE 4 Symbol of center Symbol of center depth of groove Groove depthdepth of groove Groove depth region [mm] region [mm] D30 2.180 D75 2.180D40 2.177 D85 2.177 D18 2.133 D63 2.133 D29 2.132 D74 2.132 D1 2.127 D462.127 D39 2.116 D84 2.116 D31 2.053 D76 2.053 D11 2.041 D56 2.041 D192.031 D64 2.031 D10 2.031 D55 2.031 D17 2.021 D62 2.021 D2 2.017 D472.017 D9 1.993 D54 1.993 D41 1.985 D86 1.985 D45 1.979 D90 1.979 D81.973 D53 1.973 D23 1.965 D68 1.965 D12 1.930 D57 1.930 D7 1.918 D521.918 D22 1.911 D67 1.911 D32 1.893 D77 1.893 D28 1.885 D73 1.885 D381.877 D83 1.877 D20 1.870 D65 1.870 D24 1.852 D69 1.852 D21 1.827 D661.827 D33 1.795 D78 1.795 D6 1.776 D51 1.776 D3 1.761 D48 1.761 D161.740 D61 1.740 D34 1.738 D79 1.738 D44 1.703 D89 1.703 D13 1.699 D581.699 D42 1.694 D87 1.694 D37 1.665 D82 1.665 D35 1.665 D80 1.665 D251.627 D70 1.627 D5 1.615 D50 1.615 D36 1.607 D81 1.607 D27 1.601 D721.601 D4 1.587 D49 1.587 D43 1.562 D88 1.562 D15 1.506 D60 1.506 D141.498 D59 1.498 D26 1.494 D71 1.494

(Manufacturing Example of Vibrating Plate for Comparison)

For comparison with the present invention, a vibrating plate V5 wasmanufactured through use of the same raw materials and manufacturingmethod as those of the vibrating plate V1. The center depths D₁ to D₉₀of the groove regions in the 90 portions of the vibrating plate V5 wereall set to 1.85 mm, and the vibrating plate V5 was manufactured so as tosatisfy a relationship: L_(top)/L_(btm)=1.24.

For comparison with the present invention, a vibrating plate V6 wasmanufactured through use of the same raw materials and manufacturingmethod as those of the vibrating plate V1. The center depths D₁ to D₉₀of the groove regions in the 90 portions of the vibrating plate V6 wereall set to 1.85 mm, and the vibrating plate V6 was manufactured so as tosatisfy a relationship: L_(top)/L_(btm)=4.40.

Here, the features of the vibrating plates V1, V2, V3, V4, V5, and V6are summarized in Table 5.

TABLE 5 Difference between maximum Outer Inner value and diameterdiameter Groove Local Local minimum L_(top) L_(btm) 2R 2R_(in) number XL_(top)/ maximum minimum T_(da) value of D₁ − [mm] [mm] [mm] [mm][portions] L_(btm) [pieces] [pieces] [mm] D_(x) [mm] Vibrating 1.7930.895 77.0 67.1 90 2.00 12 12 5 0.722 plate V1 Vibrating 1.897 0.79177.0 67.1 90 2.40 12 12 5 0.703 plate V2 Vibrating 1.897 0.791 77.0 67.190 2.40 12 12 6 0.724 plate V3 Vibrating 1.991 0.697 77.0 67.1 90 2.8612 12 5 0.687 plate V4 Vibrating 1.488 1.200 77.0 67.1 90 1.24 12 12 50.000 plate V5 Vibrating 1.488 0.338 77.0 67.1 90 4.40 12 12 5 0.000plate V6 Number I of groove Difference regions between between maximumlargest value and groove minimum Average region and value of D₁ − valueof D₁ second 100 × D_(x) with to D_(x) with largest |D_(sen+1) −D_(sen−1)|/ respect to D_(ave) respect to Number of groove D_(sen)T_(da) [mm] T_(da) [%] sine waves region [%] Vibrating 14.4% 1.85 37.0%4 11 0.05% plate V1 Vibrating 14.1% 1.85 37.0% 4 9 0.31% plate V2Vibrating 12.1% 1.65 27.5% 4 11 0.01% plate V3 Vibrating 13.7% 1.8537.0% 4 9 0.02% plate V4 Vibrating 0.0% 1.85 0.0% 0 0 0.00% plate V5Vibrating 0.0% 1.85 0.0% 0 0 0.00% plate V6

(Manufacturing Example and Comparative Example of Vibrator)

FIG. 12A, FIG. 12B, FIG. 12C, FIG. 12D, and FIG. 12E are each aschematic step view for illustrating an example of a method ofmanufacturing the vibrator and the ultrasonic motor of the presentinvention.

The KNN-based piezoelectric ceramics and the BCTZ-based piezoelectricceramics described in the above-mentioned manufacturing examples, andthe vibrating plates V1, V2, V3, V4, V5, and V6 were combined tomanufacture 12 vibrators. The manufacturing examples thereof are shownin Table 6.

TABLE 6 Vibrating Piezoelectric plate ceramics Manufacturing Example 1V1 KNN Example 1 Manufacturing Example 2 V2 KNN Example 2 ManufacturingExample 3 V3 KNN Example 3 Manufacturing Example 4 V4 KNN Example 4Manufacturing Example 5 V1 BCTZ Example 5 Manufacturing Example 6 V2BCTZ Example 6 Manufacturing Example 7 V3 BCTZ Example 7 ManufacturingExample 8 V4 BCTZ Example 8 Manufacturing Comparative V5 KNN Example 9Example 1 Manufacturing Comparative V6 KNN Example 10 Example 2Manufacturing Comparative V5 BCTZ Example 11 Example 3 ManufacturingComparative V6 BCTZ Example 12 Example 4

First, the annular piezoelectric ceramic piece 1021 was subjected toscreen printing of a silver paste, to thereby form the common electrode1022 on one surface as illustrated in FIG. 12C and the polarizingelectrodes 102311 in 12 portions, the non-drive phase electrodes 10232in 3 portions, and the detection phase electrode 10233 in 1 portion onthe other surface as illustrated in FIG. 12B. In this case, the distancebetween the respective adjacent electrodes illustrated in FIG. 12B wasset to 0.5 mm.

Next, polarization treatment was performed between the common electrode1022, and the polarizing electrodes 102311, the non-drive phaseelectrodes 10232, and the detection phase electrode 10233 in air throughuse of a DC power source so that the expansion and contraction polarityof the piezoelectric element became as illustrated in FIG. 4A. Thevoltage was set to a value at which an electric field of 1.0 kV/mm wasapplied, and the temperature and the voltage application time were setto 100° C. and 60 minutes, respectively. The voltage was applied duringa decrease in temperature until the temperature reached 40° C.

Next, as illustrated in FIG. 12D, in order to connect the polarizingelectrodes 102311, the connecting electrode 102312 was formed throughuse of a silver paste, and both kinds of the electrodes were combined toform the drive phase electrodes 10231 in 2 portions, to thereby providethe piezoelectric element 102. The silver paste was dried at temperaturesufficiently lower than the depolarization temperature of thepiezoelectric ceramic piece 1021. A resistance of the drive phaseelectrode 10231 was measured with a circuit tester (electric tester).One side of the circuit tester was brought into contact with the surfaceof a portion of the polarizing electrodes 102311 closest to thedetection phase electrode 10233, and the other side thereof was broughtinto contact with the surface of a portion of the polarizing electrodes102311 farthest from the detection phase electrode 10233 in thecircumferential direction of the annular shape in the drive phaseelectrode 10231. As a result, the resistance of the drive phaseelectrode 10231 was 0.6Ω.

In this stage, as a sampling inspection of the piezoelectric element102, a test piece was cut out and various characteristics of thepiezoelectric ceramic piece 1021 were evaluated. Specifically, in thepiezoelectric element 102, a rectangular strip having, for example, alength of 10 mm, a width of 2.5 mm, and a thickness of 0.5 mm was cutout from a region of one polarizing electrode 102311. The strip wasmeasured by the resonance-antiresonance method at room temperature (20°C.), to thereby obtain the piezoelectric constant d₃₁, the mechanicalquality factor Q_(m), and the Young's modulus Y₁₁. The results are shownin Table 7.

TABLE 7 Piezoelectric Mechanical constant quality factor Young's modulusKind d₃₁ [pm/V] Q_(m) [—] Y₁₁ [10⁹ Pa] KNN 100 100 95 BCTZ 95 1,200 120(Note) Measurement results at room temperature (20° C.)

Next, as illustrated in FIG. 12E, a flexible printed board 3 waspressure-bonded onto a region extending across the drive phaseelectrodes 10231 in 2 portions, the non-drive phase electrodes 10232 in2 portions, and the detection phase electrode 10233 of the piezoelectricelement 102 in a room temperature process through use of amoisture-curable epoxy resin adhesive. The flexible printed board 3 isan element to be arranged for the purpose of supplying electricity tothe electrode group and taking out a detection signal, and includeselectric wiring 301, an insulating base film 302, and a connector region(not shown) to be connected to an external drive circuit.

Next, as illustrated in FIG. 1A, the piezoelectric element 102 waspressure-bonded onto the first surface of the vibrating plate 101 (anyof V1, V2, V3, V4, V5, and V6) in a room temperature process through useof a moisture-curable epoxy resin adhesive, and the vibrating plate 101and the non-drive phase electrodes 10232 in 3 portions were connected toeach other through short-circuited wiring (not shown) formed of a silverpaste, to thereby manufacture the vibrator 1 of the present invention ora vibrator for comparison. The silver paste was dried at temperaturesufficiently lower than the depolarization temperature of thepiezoelectric ceramic piece 1021. The Young's modulus at roomtemperature of the epoxy adhesive after curing was measured inaccordance with JIS K6911 to be about 2.5 GPa.

In the vibrator 1 using the vibrating plate V1, pressure bonding wasperformed so that the 40th groove region of FIG. 7A was arranged so asto be closest to the detection phase electrode 10233. In this case, therelationship of the center depths of the 39th, 40th, and 41st grooveregions was |D₄₁−D₃₉|/D₄₀=0.05%.

In the vibrator 1 using the vibrating plate V2, pressure bonding wasperformed so that the 21st groove region of FIG. 7C was arranged so asto be closest to the detection phase electrode 10233. In this case, therelationship of the center depths of the 20th, 21st, and 22nd grooveregions was |D₂₂−D₂₀|/D₂₁=0.31%.

In the vibrator 1 using the vibrating plate V3, pressure bonding wasperformed so that the 30th groove region of FIG. 7E was arranged so asto be closest to the detection phase electrode 10233. In this case, therelationship of the center depths of the 29th, 30th, and 31st grooveregions was |D₃₁−D₂₉|/D₃₀=0.01%.

In the vibrator 1 using the vibrating plate V4, pressure bonding wasperformed so that the 36th groove region of FIG. 7G was arranged so asto be closest to the detection phase electrode 10233. In this case, therelationship of the center depths of the 35th, 36th, and 37th grooveregions was |D₃₇−D₃₅|/D₃₆=0.02%.

(Evaluation of Unnecessary Vibration Wave at Resonant Frequency ofVibrator)

The resonant frequency of the vibrator 1 of the present inventionobtained in each of the above-mentioned manufacturing examples wasmeasured, to thereby determine the number of bending vibration waves tobe generated, and a difference from the vibrator for comparison wasevaluated.

The resonant frequency was measured for each drive phase electrode(phase A and phase B) 10231. First, in order to apply an alternatingvoltage to only the phase A electrode, the phase B electrode and thedetection phase electrode 10233 were short-circuited to the non-drivephase electrode 10232 through use of the connector region of theflexible printed board 3, and the short-circuited region was connectedthrough wiring to a ground side of an external power source forevaluation. An alternating voltage having a variable frequency and anamplitude of 1 V was applied to the phase A electrode, to therebymeasure an impedance at room temperature. The frequency was changed froma high frequency side, for example, 50 kHz to a low frequency side, forexample, 1 kHz. Then, the phase A electrode and the detection phaseelectrode 10233 were short-circuited to the non-drive phase electrode10232, and an alternating voltage was applied to only the phase Belectrode. Then, frequency dependence of an impedance was similarlymeasured.

In the vibrators for comparison (Manufacturing Examples 9, 10, 11, and12) using the vibrating plate V5 or V6 in which the center depth of thegroove regions did not change, the 6th order, 7th order, and 8th orderresonant frequencies were matched between the impedance curves measuredrespectively in the phase A and the phase B. That is, it was found that,when the phase A standing wave and the phase B standing wave arecombined, the 6th order and 8th order unnecessary propagating wavesother than the desired 7th order propagating wave are also generated.

Meanwhile, in the vibrators 1 of the present invention using thevibrating plates V1, V2, V3, and V4 (Manufacturing Examples 1 to 8) inwhich the center depth of the groove regions changed in accordance withthe present invention, the desired 7th order resonant frequency wasmatched between the impedance curves measured respectively in the phaseA and the phase B, but the 6th order and 8th order unnecessary resonantfrequencies indicated different peak positions. That is, it was foundthat, when the phase A standing wave and the phase B standing wave arecombined, the generation of the 6th order and 8th order unnecessarypropagating waves is suppressed with respect to the generation of thedesired 7th order propagating wave.

(Manufacturing Example of Moving Member)

The moving member 2 was manufactured so as to be used in the ultrasonicmotor of the present invention and the ultrasonic motor for comparison.

The shape of the moving member 2 was set to an annular shape, and theouter diameter, inner diameter, and thickness thereof were set to 77.0mm, 67.1 mm, and 5 mm, respectively. An aluminum metal was used as amaterial for the moving member 2 and shaped by block machining. Then,the surface was subjected to alumite treatment.

(Manufacturing Example and Comparative Example of Ultrasonic Motor)

As illustrated in FIG. 1A and FIG. 2, the moving member 2 adjusted tothe size of the vibrating plate 101 was brought into pressure-contactwith the second surface of the vibrator 1 of the present invention, tothereby manufacture the ultrasonic motor of the present invention.Similarly, the ultrasonic motor for comparison was manufactured.

(Manufacturing Example and Comparative Example of Drive Control System)

The drive phase electrodes 10231, the non-drive phase electrodes 10232short-circuited to the common electrode 1022, and the detection phaseelectrode 10233 in the ultrasonic motor of the present invention wereelectrically connected to an external drive circuit through use of theconnector region of the flexible printed board 3, to thereby manufacturethe drive control system of the present invention having theconfiguration as illustrated in FIG. 8. The external drive circuitincludes a control unit configured to drive the ultrasonic motor and asignal generation unit configured to output an alternating voltage forgenerating a 7th order bending vibration wave in response to aninstruction of the control unit.

Similarly, a drive control system for comparison was manufactured.

(Evaluation of Maximum Rotation Speed of Ultrasonic Motor)

The maximum rotation speed of the ultrasonic motor was evaluated throughuse of the drive control systems of the present invention (drive controlsystems 1 to 8) and the drive control systems for comparison (drivecontrol systems 9 and 12).

Specifically, two kinds of loads: 150 gf·cm and 700 gf·cm were set byapplying a load to the moving member 2. Alternating voltages wereapplied to the phases A and B of the drive circuit so as to obtain anamplitude of 70 V, the same frequency, and a temporal phase differenceof π/2. Then, the maximum rotation speed of the ultrasonic motor at atime when the frequency was swept from 40 kHz to 25 kHz was evaluated.The results are shown in Table 8. In the 7th column of Table 8, areduction in maximum rotation number at a time when the load was changedfrom 150 gf·cm to 700 gf·cm is shown in terms of a percent (reductionratio (%) of the maximum rotation number).

TABLE 8 Maximum Maximum rotation rotation speed at speed at Reduction150 700 in maximum Ultrasonic L_(top)/ gf · cm gf · cm rotation Abnormalmotor Vibrator L_(btm) [rpm] [rpm] number (%) noise Drive controlUltrasonic Example 1 2.00 79 62 22% Absent system 1 motor 1 Drivecontrol Ultrasonic Example 2 2.40 82 66 20% Absent system 2 motor 2Drive control Ultrasonic Example 3 2.40 80 63 21% Absent system 3 motor3 Drive control Ultrasonic Example 4 2.86 78 60 23% Absent system 4motor 4 Drive control Ultrasonic Example 5 2.00 90 70 22% Absent system5 motor 5 Drive control Ultrasonic Example 6 2.40 92 74 20% Absentsystem 6 motor 6 Drive control Ultrasonic Example 7 2.40 90 71 21%Absent system 7 motor 7 Drive control Ultrasonic Example 8 2.86 90 6923% Absent system 8 motor 8 Drive control Ultrasonic Comparative 1.24 6820 71% Present system 9 motor 9 Example 1 Drive control UltrasonicComparative 4.40 60 40 33% Present system 10 motor 10 Example 2 Drivecontrol Ultrasonic Comparative 1.24 75 25 67% Present system 11 motor 11Example 3 Drive control Ultrasonic Comparative 4.40 74 45 39% Presentsystem 12 motor 12 Example 4

The drive control systems using the vibrators and the ultrasonic motorsof the Examples exhibited maximum rotation speeds of the ultrasonicmotor higher than those of the drive control systems for comparison inboth the cases of 150 gf·cm and 700 gf·cm. In Comparative Examples 1 to4 using the vibrating plates V5 and V6, the reduction ratio of arotation speed at a time when the load was changed from 150 gf·cm to 700gf·cm was large, and the reduction ratio was large particularly inComparative Examples 1 and 3.

In the Examples, equivalent rotation drive was observed in any rotationdirection, and abnormal noise was not generated during rotation drive.After the test, the moving member 2 was removed, and the shapes of theprotrusion regions 1011 of the vibrating plate 101 were checked.However, no loss caused by abrasion was observed.

Meanwhile, in the drive control systems for comparison, abnormal noisewas generated during rotation drive.

(Manufacturing Example of Optical Apparatus)

The optical apparatus illustrated in FIG. 9A and FIG. 9B, and FIG. 10was manufactured through use of the drive control system of the presentinvention, and an autofocus operation in accordance with the applicationof an alternating voltage was checked. Even in a high load, theautofocus speed was sufficiently higher than that of the opticalapparatus of Comparative Examples.

According to the present invention, there can be provided an ultrasonicmotor configured to rotate a moving member with a 7th order bendingvibration wave, in which a desired drive speed is exhibited withsufficient torque even when lead-free piezoelectric ceramics having highenvironmental safety is used, a drive control system and an opticalapparatus that use the ultrasonic motor, and a vibrator to be used inthe ultrasonic motor.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2015-231902, filed Nov. 27, 2015, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An ultrasonic motor, comprising: an annularvibrator; and an annular moving member arranged so as to be brought intopressure-contact with the annular vibrator, wherein the annular vibratorcomprises: an annular vibrating plate; and an annular piezoelectricelement arranged on a first surface of the annular vibrating plate, theannular vibrating plate being brought into contact with the annularmoving member on a second surface on a side opposite to the firstsurface, wherein the annular piezoelectric element comprises: an annularpiezoelectric ceramic piece; a common electrode arranged on a surface ofthe annular piezoelectric ceramic piece opposed to the annular vibratingplate so as to be sandwiched between the annular piezoelectric ceramicpiece and the annular vibrating plate; and a plurality of electrodesarranged on a surface of the annular piezoelectric ceramic piece on aside opposite to the surface on which the common electrode is arranged,wherein the annular piezoelectric ceramic piece contains lead in acontent of less than 1,000 ppm, wherein the plurality of electrodescomprise two drive phase electrodes, one or more non-drive phaseelectrodes, and one or more detection phase electrodes, wherein thesecond surface of the annular vibrating plate includes groove regionsextending radially in X portions, and when an outer diameter of theannular vibrating plate is set to 2R in a unit of mm, the X is a naturalnumber satisfying 2R/0.85−5≦X≦2R/0.85+15 and the outer diameter 2R is 57mm or more, wherein a ratio between an average value L_(top) of a lengthin a circumferential direction on an outer diameter side of a wallregion that separates the adjacent groove regions from each other and anaverage value L_(btm) of a length in a circumferential direction on anouter diameter side of the groove regions falls within a range of2.00≦L_(top)/L_(btm)≦2.86, and wherein, when center depths of the grooveregions in the X portions are represented by D₁ to D_(X) in order in thecircumferential direction, the D₁ to the D_(X) change so as to follow acurve obtained by superimposing one or more sine waves on one another,the groove regions reaching a local maximum in 12 or more regions in thechange of the center depth and the groove regions reaching a localminimum in 12 or more regions in the change of the center depth, thegroove regions reaching the local maximum and the groove regionsreaching the local minimum being prevented from being adjacent to eachother.
 2. An ultrasonic motor according to claim 1, wherein the annularpiezoelectric ceramic piece has a Young's modulus at room temperature of80 GPa or more and 125 GPa or less.
 3. An ultrasonic motor according toclaim 1, wherein the D₁ to the D_(X) has a difference between a maximumvalue and a minimum value of 5% or more and 25% or less with respect toa maximum thickness T_(dia) of the annular vibrating plate.
 4. Anultrasonic motor according to claim 1, wherein the D₁ to the D_(X) havea standard depth D_(ave) of 25% or more and 50% or less with respect tothe maximum thickness T_(dia).
 5. An ultrasonic motor according to claim1, wherein, when a length of one arc, which is obtained by dividing acircumference of a circle that passes through an arbitrary position on asurface of the annular piezoelectric element and shares a center withthe annular piezoelectric element by seven, is represented by λ and acircumferential length of the circle is represented by 7λ, the two drivephase electrodes each have a circumferential length of 3λ and areseparated from each other in the circumferential direction by twospacing regions respectively having lengths of λ/4 and 3λ/4 in thecircumferential direction, the annular piezoelectric ceramic piece in aregion brought into contact with each of the drive phase electrodescomprising six polarized regions in which polarity is reversedalternately in the circumferential direction, the one or more non-drivephase electrodes and the one or more detection phase electrodes beingarranged in the two spacing regions.
 6. An ultrasonic motor according toclaim 1, wherein the outer diameter 2R of the annular vibrating plate is90 mm or less.
 7. An ultrasonic motor according to claim 1, wherein theannular vibrating plate has an inner diameter 2R_(in) in a unit of mm,which satisfies a relationship: 2R−16≦2R_(in)≦2R−6.
 8. An ultrasonicmotor according to claim 1, wherein the annular piezoelectric ceramicpiece has an outer diameter smaller than the outer diameter of theannular vibrating plate, and the annular piezoelectric ceramic piece hasan inner diameter larger than an inner diameter of the annular vibratingplate.
 9. An ultrasonic motor according to claim 1, wherein the annularvibrating plate has a maximum thickness T_(dia) of 4 mm or more and 6 mmor less.
 10. An ultrasonic motor according to claim 1, wherein theannular vibrating plate is made of an alloy containing 50 mass % or moreof steel and 10.5 mass % or more of chromium.
 11. An ultrasonic motoraccording to claim 1, wherein the X represents an even number, and ofthe D₁ to the D_(X), a depth change of D₁ to D_(X/2) and a depth changeof D_(X/2+1) to D_(X) are matched with each other.
 12. An ultrasonicmotor according to claim 1, wherein, when a center depth of the grooveregion closest to the detection phase electrode is represented byD_(sen), where sen is a natural number satisfying X≧sen,(D_(sen+1)−D_(sen−1))/D_(sen) is 5% or less.
 13. An ultrasonic motoraccording to claim 1, wherein, of the groove regions reaching the localmaximum, the groove regions have a center depth that is 1.15 times ormore and 1.30 times or less of a standard depth D_(ave) in at least 8regions.
 14. An ultrasonic motor according to claim 1, wherein, of thegroove regions reaching the local maximum, a number I of the grooveregions positioned between the groove region having a largest centerdepth and the groove region having a second largest center depthsatisfies a relationship: I≧X/18.
 15. An ultrasonic motor according toclaim 1, wherein the groove regions reach the local maximum of thecenter depth in from 12 portions to 16 portions.
 16. An ultrasonic motoraccording to claim 1, wherein the annular piezoelectric ceramic piececomprises a perovskite type metal oxide represented by one of thefollowing general formulae (1) and (2) as a main component, and acontent of metal components other than the main component contained inthe annular piezoelectric ceramic piece is 1 part by weight or less interms of a metal with respect to 100 parts by weight of the perovskitetype metal oxide:{M_(h)(Na_(j)Li_(k)K_(1-j-k))_(1-h)}_(1-m){(Ti_(1-u-v)Zr_(u)Hf_(v))_(h)(Nb_(1-w)Ta_(w))_(1-h)}O₃  (1)where M represents at least one kind selected from the group consistingof (Bi_(0.5)K_(0.5)), (Bi_(0.5)Na_(0.5)), (Bi_(0.5)Li_(0.5)), Ba, Sr,and Ca, and 0.06<h≦0.3, 0≦j≦1, 0≦k≦0.3, 0≦j+k≦1, 0<u≦1, 0≦v≦0.75,0≦w≦0.2, 0<u+v≦1, and −0.06≦m≦0.06; and(Ba_(1-s)Ca_(s))_(α)(Ti_(1-t)Zr_(t))O₃  (2) where 0.986≦α≦1.100,0.025≦s≦0.30, and 0.020≦t≦0.095.
 17. A drive control system, comprisingat least an ultrasonic motor, comprising: an annular vibrator; and anannular moving member arranged so as to be brought into pressure-contactwith the annular vibrator, wherein the annular vibrator comprises: anannular vibrating plate; and an annular piezoelectric element arrangedon a first surface of the annular vibrating plate, the annular vibratingplate being brought into contact with the annular moving member on asecond surface on a side opposite to the first surface, wherein theannular piezoelectric element comprises: an annular piezoelectricceramic piece; a common electrode arranged on a surface of the annularpiezoelectric ceramic piece opposed to the annular vibrating plate so asto be sandwiched between the annular piezoelectric ceramic piece and theannular vibrating plate; and a plurality of electrodes arranged on asurface of the annular piezoelectric ceramic piece on a side opposite tothe surface on which the common electrode is arranged, wherein theannular piezoelectric ceramic piece contains lead in a content of lessthan 1,000 ppm, wherein the plurality of electrodes comprise two drivephase electrodes, one or more non-drive phase electrodes, and one ormore detection phase electrodes, wherein the second surface of theannular vibrating plate includes groove regions extending radially in Xportions, and when an outer diameter of the annular vibrating plate isset to 2R in a unit of mm, the X is a natural number satisfying2R/0.85−5≦X≦2R/0.85+15 and the outer diameter 2R is 57 mm or more,wherein a ratio between an average value L_(top) of a length in acircumferential direction on an outer diameter side of a wall regionthat separates the adjacent groove regions from each other and anaverage value L_(btm) of a length in a circumferential direction on anouter diameter side of the groove regions falls within a range of2.00≦L_(top)/L_(btm)≦2.86, and wherein, when center depths of the grooveregions in the X portions are represented by D₁ to D_(X) in order in thecircumferential direction, the D₁ to the D_(X) change so as to follow acurve obtained by superimposing one or more sine waves on one another,the groove regions reaching a local maximum in 12 or more regions in thechange of the center depth and the groove regions reaching a localminimum in 12 or more regions in the change of the center depth, thegroove regions reaching the local maximum and the groove regionsreaching the local minimum being prevented from being adjacent to eachother; and a drive circuit electrically connected to the ultrasonicmotor.
 18. A drive control system according to claim 17 wherein thedrive circuit comprises a signal generation unit configured to generatea 7th order bending vibration wave in the annular vibrator.
 19. Anoptical apparatus, comprising at least a drive control system,comprising at least an ultrasonic motor, comprising: an annularvibrator; and an annular moving member arranged so as to be brought intopressure-contact with the annular vibrator, wherein the annular vibratorcomprises: an annular vibrating plate; and an annular piezoelectricelement arranged on a first surface of the annular vibrating plate, theannular vibrating plate being brought into contact with the annularmoving member on a second surface on a side opposite to the firstsurface, wherein the annular piezoelectric element comprises: an annularpiezoelectric ceramic piece; a common electrode arranged on a surface ofthe annular piezoelectric ceramic piece opposed to the annular vibratingplate so as to be sandwiched between the annular piezoelectric ceramicpiece and the annular vibrating plate; and a plurality of electrodesarranged on a surface of the annular piezoelectric ceramic piece on aside opposite to the surface on which the common electrode is arranged,wherein the annular piezoelectric ceramic piece contains lead in acontent of less than 1,000 ppm, wherein the plurality of electrodescomprise two drive phase electrodes, one or more non-drive phaseelectrodes, and one or more detection phase electrodes, wherein thesecond surface of the annular vibrating plate includes groove regionsextending radially in X portions, and when an outer diameter of theannular vibrating plate is set to 2R in a unit of mm, the X is a naturalnumber satisfying 2R/0.85−5≦X≦2R/0.85+15 and the outer diameter 2R is 57mm or more, wherein a ratio between an average value L_(top) of a lengthin a circumferential direction on an outer diameter side of a wallregion that separates the adjacent groove regions from each other and anaverage value L_(btm) of a length in a circumferential direction on anouter diameter side of the groove regions falls within a range of2.00≦L_(top)/L_(btm)≦2.86, and wherein, when center depths of the grooveregions in the X portions are represented by D₁ to D_(X) in order in thecircumferential direction, the D₁ to the D_(X) change so as to follow acurve obtained by superimposing one or more sine waves on one another,the groove regions reaching a local maximum in 12 or more regions in thechange of the center depth and the groove regions reaching a localminimum in 12 or more regions in the change of the center depth, thegroove regions reaching the local maximum and the groove regionsreaching the local minimum being prevented from being adjacent to eachother; and a drive circuit electrically connected to the ultrasonicmotor; wherein the drive circuit comprises a signal generation unitconfigured to generate a 7th order bending vibration wave in the annularvibrator; and an optical element dynamically connected to the ultrasonicmotor.
 20. An annular vibrator, comprising: an annular vibrating plate;and an annular piezoelectric element arranged on a first surface of theannular vibrating plate, wherein the annular piezoelectric elementcomprises: an annular piezoelectric ceramic piece; a common electrodearranged on a surface of the annular piezoelectric ceramic piece opposedto the annular vibrating plate so as to be sandwiched between theannular piezoelectric ceramic piece and the annular vibrating plate; anda plurality of electrodes arranged on a surface of the annularpiezoelectric ceramic piece on a side opposite to the surface on whichthe common electrode is arranged, wherein the annular piezoelectricceramic piece contains lead in a content of less than 1,000 ppm, whereinthe plurality of electrodes comprise two drive phase electrodes, one ormore non-drive phase electrodes, and one or more detection phaseelectrodes, wherein a second surface of the annular vibrating plateincludes groove regions extending radially in X portions, and when anouter diameter of the annular vibrating plate is set to 2R in a unit ofmm, the X is a natural number satisfying 2R/0.85−5≦X≦2R/0.85+15 and theouter diameter 2R is 57 mm or more, wherein a ratio between an averagevalue L_(top) of a length in a circumferential direction on an outerperipheral side of a wall region that separates the adjacent grooveregions and an average value L_(btm) of a length in a circumferentialdirection on an outer peripheral side of the groove regions is2.00≦L_(top)/L_(btm)≦2.86, and wherein, when center depths of the grooveregions in the X portions are represented by D₁ to D_(X) in order in thecircumferential direction, the D₁ to the D_(X) change so as to follow acurve obtained by superimposing one or more sine waves on one another,the groove regions reaching a local maximum in 12 or more regions in thechange of the center depth and the groove regions reaching a localminimum in 12 or more regions in the change of the center depth, thegroove regions reaching the local maximum and the groove regionsreaching the local minimum being prevented from being adjacent to eachother.